72. If we go on littering the environment (become) ______ seriously polluted.

76-77. Don't worry. If we (not/understand) ____ the lesson, the teacher (explain)____  it again.

79. Can you remember what you (wear) ____ the night you lost your phone. 

1. Hoa (work) ______ very hard recently.

2. I (do)______ my home work when the earthquake happened

3. There (be) _______ great changes in my country in the past few years.

4. He (start) ____ learning English when he was in grade 3.

5. They (be) ready in a moment. Let's wait for them.

6.  What time the banks here (open) _______?

7.Listen! Someone (knock)_______ the door.

8. I (wait) _______ the bus stop when I saw him going past.

9-10-11. They still (live) ______ in a small house now but they (move) ______ to a bigger one right after they (finish) ______.