Ответ:

1. By the time I was ten I had travelled to 20 countries.

2. They were late because they had met a friend on the way.

3. Before I went out, I had cleaned my room and done all my homework.

4. I couldn't call you because I had been visiting my doctor.

5. When I read the email, I realized that he had not done anything to improve his writing skills.

Объяснение: