Read the passage and choose the correct answer for the gaps 29-31 in t

A) whom

139. (v12z-104-29) Read the passage and choose the correct answer for the gaps 29-31 in the text. I work in a large office with about thirty other people, most of (29)... I know quite well. In fact, most of my colleagues are so interesting that I (30)... of writing a book about them. One of the sales representatives, Keith, is (31)... Betty from overseas department. And plenty of other things are going on. A) whom B) which C)who
D) whose