a) 1. I don't have enough time today to prepare well for the lesson, let alone to go to the country. 2. He didn't know her name, let alone her address. 3. I didn't have time even to ring him up, let alone to come to his place
b) 1. They started early as usual. 2. At last the bus started 3. We'll start the discussion as soon as they come.
c) 1. He has already Written part of the article 2. They have already finished part of the work 3. The second part of the book is not so interesting as the first one. 4. Are all of you going to take part in the discussion?