1,
a, is the most crowded city in Vietnam. (so sánh nhất của tính từ dài: tobe + the most + adj + N)
b, the first time I have ever tasted fish and chips. (thì hiện tại hoàn thành: S + have/has + V_ed/P2)
c, seen her mother for five months. (thì hiện tại hoàn thành: S + have/has (not) + V_ed/P2 + for + khoảng thời gian)
d, watching fireworks at night. (enjoy + V_ing: thích làm gì)
2,
a) What is your favourite TV program?
b) Pele-king of football won the first World Cup at the age of 17.
c) The Eiffel Town is the world's second most visited tourist place.
d) I think we might travel to the Moon in the future.
e) Noise pollution cause hearing problems.
3,
a, There might not the meeting this afternoon because the director is ill.
b) It will be holiday tomorrow so the workers don't have to go to work.