people have always been curious ______ how living things on the earth exactly began.
| A．in | B．at | C．of | D．about |
A lot of children never fully ______ their mothers until it is too late.
| A．urge | B．appreciate | C．accuse | D．motivate |
______ I admit that there are problems, I don't agree that they cannot be solved.
| A．As | B．If | C．While | D．When |
Small _____ it is, the pen is a most useful tool.
| A．because | B．so | C．if | D．as |
______ it is getting dark.，we’d better hurry
| A．And | B．But | C．Since | D．Unless |
_____ she was very tired, she went on working.
| A．As | B．Although | C．Even | D．In spite of |