In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank. I was often invited to colleges and universities (1) ______ lectures. Once, I went to a university to deliver a lecture. (2) ______, it was over, the students gathered to ask (3) ______ questions. Though it was getting late (4) ______ my next programme, since I love talking to (5) ______, I remained there answering their questions. Select the most appropriate option to fill in blank No. 4.

1. A
   at
2. B
   to
3. C
   for
4. D
   on