We must do everything we can _____ our earth cleaner and safer.
| A．made | B．to making |
| C．make | D．to make |
The Great Wall is famous lots of visitors all over the world come to visit it every year.
| A．so; that | B．such; that |
| C．enough; that | D．very; that |
__________ it’s very difficult, remember not to give up until the last minute.
| A．Until | B．Unless | C．Although | D．Since |
You will never know the result ______ you try it by yourself.
| A．when | B．if | C．unless | D．after |
________ he told the truth this time, nobody was willing to believe him because he often told lies.
| A．When | B．Because | C．Although | D．Unless |
___________ you do, remember to look after your parents well.
| A．Whatever | B．Wherever |
| C．Whoever | D．Whenever |