I had to buy ________ these books because I didn't know which one was the best.

 I've achieved a lot in my study, thanks to ____ who helped me.

—What do you think of the four classics(名著) of China? —I hear they are wonderful, but I’ve read _____ of them.

He had lost his temper and his health in the war and never found ____ of them again.

I don’t think ___ possible to travel around the world without any modern equipment．