I regret ___ harder in the past two years.
| A．not having studied | B．having studied | C．having not studied | D．not being studied |
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 |
This is the factory my father worked ten years ago.
| A．where | B．that | C．which | D．when |
He tried his best to solve the problem, difficult it was.
| A．no matter what | B．whatever | C．however | D．how |