Not until the teacher explained the importance of getting up early ______ we promise to come early.
| A．should | B．would | C．did | D．could |
_______you study hard，you’ll succeed in time.
| A．As far as | B．As long as |
| C．As good as | D．As well as |
He tried his best to solve the problem，________difficult it was.
| A．however | B．no matter |
| C．whatever | D．although |
Measures have been taken to prevent the river from____．
| A．having polluted | B．being polluting |
| C．being polluted | D．to pollute |
Children often display an________curiosity about every new thing they encounter.
| A．impossible | B．unreliable |
| C．extra | D．incredible |
___________in reality，the story is popular with adults.
| A．Root | B．Rooting |
| C．Rooted | D．To root |