**Question 15:**
Da Nang has replaced Hoi An as a hub for shipping business.
**D. remained**
"Remained" fits best in the context of replacing something. Da Nang replacing Hoi An suggests that Hoi An was once a hub but Da Nang now is.
**Question 16:**
I had to finish my assignment, so I went to bed late last night.
**A. stayed up late**
"Stayed up late" means remaining awake later than usual, which fits the context of finishing an assignment.
**Question 17:**
They have contributed to making the unique Vietnamese culture, and strengthening
**D. making more forceful**
"Making more forceful" is appropriate for strengthening the unique Vietnamese culture.
**Question 18:**
That extra CO2 is the result of man-made pollution.
**B. enormous**
"Enormous" describes the significant amount of extra CO2 resulting from man-made pollution.
**Question 19:**
I am really excited about visiting Ho Chi Minh museum.
**A. I'm looking forward to visiting Ho Chi Minh museum.**
This option correctly conveys excitement about a future event. Note: There is a typo in the options; the correct answer should be "**A. I'm looking forward to visiting Ho Chi Minh museum.**"
**Question 20:**
She said to us "Keep quiet in the classroom!"
**C. She told us to keep quiet in the classroom.**
This is the correct reported speech form for the imperative sentence.
**Question 21:**
I often stay up late in the evening.
**A. I am used to staying up late in the evening.**
This choice accurately reflects a habitual action using the correct grammatical structure.