1. He believed... no, he was sure that he had been there before.
2. I've been trying to find you all morning. Where have you been? What have you been doing?
3. In a week at the same time I won't be studying. I will be swimming and lying on the beach.
4. Brian was reading a letter. He had been reading it for as long as 15 minutes, but the handwriting was so illegible that it was very difficult to read.