Scientists think they have _____ in their attempt to find the causes of some major dieases.

____ do you join the club —Because I like music.

7．He visited the Effel Tower, which_____________to 1889, during his stay in France last summer.

My parents always tell me ___ others late at night.– They’re right. It’s not polite.

I’d like to call you at 10 o’clock next Friday morning if it is convenient.—I’m afraid I _______ an important meeting