---Which of the three optional courses did you like best, Joe? ---To tell you the truth, I didn’t like _______ of them.

---Which book do you think is the most useful to my studies?---________, as long as you read it. In fact, they are out of date.

You may depend_______it won’t happen again.

—Which of the two pens are you going to buy?—I’ll buy _____of them, so I can give one to my friend.

She owns a lot of books, most of _____ are written in English.