Low-carbon lifestyle is of great benefit to improve the world environment, but the problem is difficult to _________．

I __________ there little more than a week when I set to work with the scientist

The university started some new language programs to _____ the country’s Silk Road Economic Belt.

Will $200________ ? —I’m afraid not . We need at least 50 more dollars .

It will______us several years to learn a foreign language well.