—Which tie do you prefer, sir?     —I’ll take ____ to have a change sometimes.

—Mary，new copies of 《Harry Potter》 are on sale now．—Great! Let’s go and buy       this afternoon．

I’d appreciate __________ if you could lend me a hand with my homework.

I wanted to buy a comic book for my cousin,but there was_______left in the shop.

It is so difficult a problem that _____ student in this class _____ work it out.