______ studying abroad can be hard， it can broaden your understanding of the world.
| A．If | B．While |
| C．Because | D．Since |
One learns a language by making mistakes and ______ them.
| A．corrects | B．correct | C．to correct | D．correcting |
By the time you have finished this book, your meal ______ cold.
| A．gets | B．has got | C．will get | D．is getting |
—It’s a long time________I saw you last.
—Yes，and what a pity it is now that it will be a long time________we see each other again.
| A．before；since | B．since；when | C．since；before | D．when；before |
The factory produces two million pairs of shoes every year, half _______ are sold abroad.
| A．of which | B．which of | C．of them | D．of that |
We should develop the sunshine project actively, because it can save _______ resources as well as reduce pollution.
| A．power | B．strength | C．force | D．energy |