1. It was an extremely frightened experience in my life.
-> frightening -> vật (tính từ đuôi ing)
2. Mark went on working despite he felt unwell.
-> although -> although + S + V = despite + N/Ving : mặc dù
3. My sister had worked in the bank for five years before she had been sent to Da Nang.
-> was
4. Tom said that he had been very excited visiting Ha Long Bay for the first time in 2005.
-> to visit. Vì excited là tính từ ta sử dụng cấu trúc: It's + adj + to + V-infinitive
5. The country has significant changed since we came here in 2007.
-> Significantly. Vì sau đt là trạng từ