To protect the environment, the local government has ______ a lot of signs to warn the citizens not to litter the ground.
| A．add up | B．take up |
| C．set up | D．put up |
He was made _____.
| A．go | B．gone |
| C．going | D．to go |
Returning to the room, _____.
| A．the book was lost | B．I found the book missing |
| C．the book was missing | D．I found the losing book |
_________ in the fields on a March afternoon，he could feel the warmth of spring．
| A．To walk | B．Walking |
| C．Walked | D．Having walked |
He was busy writing a story，only _________ once in a while to smoke a cigarette．
| A．to stop | B．stopping |
| C．to have stopped | D．having stopped |