18. Chứng minh rằng các phân số sau là phân số tối giản với mọi số tự nhiên n:   
\(\dfrac{ n+1}{2n+3 }\) ý a

\(\dfrac{ 2n+3}{4n+8 }\)ý b

\(\dfrac{ 3n+2}{ 5n+3}\) ý c

Up     Recycling             from            take             and

(1) ___________ is using rubbish to remake new goods that can be sold again. For example, when you put bottles and cans in the recycling bin, people (2) ___________ them to a factory. In this factory, people reprocess these bottles (3) ___________cans into many new things.

Recycling starts when you or your parents drop recyclable materials, such as bottles and cans in the recycling bin. Next, collectors come to pick (4)___________ the materials and take them to a processing factory where they are sorted and processed into raw materials. After that, factories sell these materials to manufacturers who make the things you buy. These manufacturers make new items from them. Finally, you or your parents buy items made (5) ___________ recycled materials.

giúp mk vs