问题

Scientists have to work hard to keep_____ with modern discoveries and developments

A:carried it off
B:carry it off
C:had carried it off
D:have carried it off

正确答案是：

同类题型

1． I don’t think there is _______ with thecomputer.

Some of the apples are bad, but I believe the rest sweet.

We ______ him to stop surfing the Internet, but he wouldn’t.

Look! Here _____ another bus. Let’s get on it.[ ]

know Mr. Green has been ill for days— Yes, I wonder if he is ______ better now.