Một ngày con sên bò được số mét là:

$3-1=2(m)$

Số ngày mà con sên cần để bò lên khỏi giếng là:

$13:2=6$ (dư 1) (ngày)

Đáp số: 7 ngày.

1. was thinking - called

2. was - was bitten

3. was caught

4. invited - didn't invite

Căn thức có nghĩa $\Leftrightarrow 9x^2-6x+1 ≥0 \Leftrightarrow (3x-1)^2≥0 \forall x$

Vậy căn thức có nghĩa với mọi x.

1. She likes to be a doctor in the future because she likes looking after patients.

1. to forgive - has done
2. have attended
3. are having - are spending
4. did she come
5. is going to build - welcome
6. is never - will come
7. are working
7. seeing
9. completed
10. Did they sell
12. have ever trained
13. asked - to leave
14. has advised - to take 
15. has sat - came
16. to have

2. John likes to become an architect in the future because he likes designing buildings

3. What will you like to be in the future?

10. fast-dangerous

1. B
2. D
3. D
4. C
5. B
6. A
7. D
8. C
9. B