This is the second time I have seen her (twice)

If she doesnt try her best,she will fail the exam (unless)

It is agaist the rules to park her (mustnt)

He cant drive a car (possible)

SOSSSSS

1. i have seen have twice.

-> S + have/has + V p.p + số lần : đã từng làm gì bao nhiêu lần

2.  unless she tries her best, she will fail the exam.

-> câu điều kiện loại  1:  If/ Unless+  S+V(s/es), S + will +V-inf

  chú ý : unless = if ...not

3.you mustn't park here.

-> S + mustn't + V-inf  : ko đc lmj

4. it's possible for him to drive a car.

-> it's + adj + (for sb) + to-V  :  lmj đó đối vs ai ntn đó