50. The exercise/ give / yesterday / teacher / difficult.
A. The exercise gave yesterday by the teacher was difficult.
B. The exercise given yesterday by the teacher is difficult.
C. The exercise was given yesterday by the teacher was difficult.
D. The exercise giving yesterday by the teacher is difficult.

⇒ Vì câu này chia đúng dạng của dộng từ là ở thì quá khứ
45. Let’s go somewhere for a drink.
A. What about going somewhere for a drink? 
B. What about to go somewhere for a drink?
C. What about go somewhere for a drink? 
D. What about going to somewhere for a drink?

=> Vì ta có mẫu câu: What about + cụm(danh từ)/ V-ing? và cụm cố định "go to + địa điểm" để nói rằng đi đến đâu đó

41. Tom has not been seen by my father yet.

A. Tom has not seen my father yet.

B. My father has not been seen Tom yet.

C. My father has not seen Tom yet.

D. My father has not yet seen Tom

=> Vì ta có công thức thì hiện tại hoàn thành là: 

+) S+have/has+phân từ 2+...

-) S+haven't/hasn't+phân từ 2+....

?) Have/has+S+phân từ 2+....?