Dưới đây là các câu đã được sửa lỗi:

1. The first time they saw the ocean, they **had** never been to the beach before.
2. Sarah **started** learning piano 3 years ago. (Hoặc: Sarah **has been** learning piano for 3 years.)
3. The last time we visited our grandparents was last year, and we **have not** seen them since.
4. The first time Jack **ate** sushi was amazing; he **had** never tasted anything like it before.
5. The team **had been working** on this project for five months when they received a promotion.
6. The last time she saw a concert was in 2019, but she **has not gone** to any concerts since.
7. The first time they **traveled** abroad, they were really excited.
8. Tom started to learn Spanish **two years ago**. (Hoặc: Tom has been learning Spanish for two years.)
9. The last time we went hiking was two months ago, and we **have not gone** since.
10. The first time Emma tried ice cream was in her childhood; she **had** never tasted anything similar after that.

Các lỗi chủ yếu liên quan đến thì (tense), sử dụng "since" và "for" không đúng ngữ cảnh, và chỉnh sửa một số từ để cho câu có nghĩa chính xác hơn.