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 |
Distinguished guests and friends, welcome to our school. the ceremony of the 50th Anniversary this morning are our alumni（校友） from home and abroad.
| A．Attend | B．To attend | C．Attending | D．Having attended |
I like getting up very early in summer. The morning air is so good .
| A．to be breathed | B．to breathe | C．breathing | D．being breathed |
The wet weather will continue tomorrow, when a cold front to arrive.
| A．is expected | B．is expecting | C．expects | D．will be expected |
When he the door, he found his keys were nowhere.
| A．would open | B．opened | C．had opened | D．was to open |