Помогите с выбором правильной формы глагола

1. He … the house before I had time to ask him anything.
a) left b) was leaving c) had left
2. When I rang up Mike, he … still … the poem.
a) did … learnt b) was … learning c) had learnt
3. I … to the hotel after I had sent the telegram to my relatives.
a) returned b) was returning c) had returned
4. While Kate … in America, she learnt a lot about a famous pop star Madonna.
a) travelled b) was travelling c) had traveled
5. When … you … receive a letter from your friend?
a) did … receive b) were … receiving c) had … received