Thanh OA có khối lượng không đáng kể, có chiều dài 20cm, quay dễ dàng quanh trục nằm ngang O. Một lò xo gắn vào điểm giữa C. Người ta tác dụng vào đầu A của thanh một lực  F = 20 N hướng thẳng đứng xuống dưới. Khi thanh ở trạng thái cân bằng, lò xo có hướng vuông góc với OA, và OA làm với đường nằm ngang một góc α = 30 ∘ . Tìm phản lực N của lò xo lên thanh.

A. 45 2 N                                                

B. 20 3 N         

C. 20 2 N

D. 35 3 N

Read the passage and mark A, B, C or D to indicate the correct answer to each of the questions.

 Jupiter is the largest and most massive planet and is fifth in order of distance from the sun. It is well placed for observation for several months in every year and on average is the brightest of the planets apart from Venus, though for relatively brief periods Mars may outshine it. Jupiter’s less than 10 hour rotation period gives it the shortest day in the solar system in so far as the principal planets are concerned. There are no true seasons on Jupiter because the axial inclination to the perpendicular of the orbital plane is only just over 3°-less than that for any other planet.

 The most famous mark on Jupiter is the Great Red Spot. It has shown variations in both intensity and color, and at times it has been invisible, but it always returns after a few years. At its greatest extent it may be 40,000 kilometers long and 14,000 kilometers wide, so its surface area is greater than that of Earth. Though the latitude of the Red Spot varies little, it drifts about in longitude. Over the past century the total longitudinal drift has amounted to approximately 1200°. The latitude is generally very close to -22°. It was once thought that the Red Spot might be a solid or semisolid body floating in Jupiter’s outer gas. However, the Pioneer and Voyager results have refuted that idea and proven the Red Spot to be a phenomenon of Jovian meteorology. Its longevity may well due to its exceptional size, but there are signs that it is decreasing in size, and it may not be permanent. Several smaller red spots have been seen occasionally but have not lasted.
Question:The word “exceptional” in paragraph 2 mostly means _______

A. extreme

B. sustainable

C. temporary

D. infrequent

Mark the letter A, B, C, D on your answer sheet to indicate the correct answer to each of the following questions

The house still remains in ___ after the hurricane

A. a good condition 

B. good condition

C. good conditions

D. the good condition

Mark the letter A, B, C or D on your answer sheet to indicate the correct answer for each of the blanks.
A few natural elements exist in _______ that they are rarely seen in their natural environments.

A. such small quantities

B. so small quantities

C. very small quantities

D. small quantity

Read the following passage and choose the letter A, B, C or D to answer the comprehension questions

Are organically grown foods the best food choices? The advantages claimed for such foods over conventionally grown and marketed food products are now being debated. Advocates of organic foods - a term whose meaning varies greatly - frequently proclaim that such products are safer and more nutritious than others.

The growing interest of consumers in the safety and nutritional quality of the typical North American diet is a welcome development. However, much of this interest has been sparked by sweeping claims that the food supply is unsafe or inadequate in meeting nutritional needs. Although most of these claims are not supported by scientific evidence, the preponderance of written material advancing such claims makes it difficult for the general public to separate fact from fiction. As a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore.

Almost daily the public is besieged by claims for “no-aging” diets, new vitamins, and other wonder foods. There are numerous unsubstantiated reports that natural vitamins are superior to synthetic ones, that fertilized eggs are nutritionally superior to unfertilized eggs, that untreated grains are better than fumigated grains, and the like.

One thing that most organically grown food products seem to have in common is that they cost more than conventionally grown foods. But in many cases consumers are misled if they believe organic foods can maintain health and provide better nutritional quality than conventionally grown foods. So there is real cause for concern if consumers, particularly those with limited incomes, distrust the regular food supply and buy only expensive organic foods instead.

According to the last paragraph, consumers who believe that organic foods are better than conventionally grown foods are often ______.

A. careless

B. mistaken

C. economical

D. wealthy

Chất hữu cơ X chứa vòng benzen có công thức phân tử là C x H y O . Biết % O   =   14 , 81 % (theo khối lượng). Số công thức cấu tạo phù hợp của X là

A. 8.

B. 6.

C. 7.

D. 5.

Đốt cháy hoàn toàn 6,75 gam hỗn hợp E chứa 3 este đều đơn chức, mạch hở cần vừa đủ 8,904 lít O₂ (đktc) thu được CO₂ và 4,95 gam H₂O. Mặt khác, thủy phân hoàn toàn lượng E trên bằng dung dịch chứa NaOH (vừa đủ) thu được 2 ancol (no, đồng đẳng liên tiếp) và hai muối X, Y có cùng số C (M_X>M_Y và n_X <n_Y) . Đốt cháy hoàn toàn lượng ancol trên cần vừa đủ 0,18 mol O₂. Tỷ số n_X:n_Y là?

A. 11:17

B. 4:9 

C. 3:11       

D. 6:17