下列说法正确的是（ ）
| A．重力对物体做功与路径无关，只与始末位置有关。 |
| B．滑动摩擦力一定对物体做负功 |
| C．合外力做功为零，物体机械能一定不变 |
| D．若物体受到的合外力不为零，则物体的机械能一定变化 |
-----_____ leave at the end of this month.
-------I don’t think you should do that until _____ another job.
| A．I’m going to; you’d found | B．I’m going to; you’ve found |
| C．I’ll; you’ll find | D．I’ll; you’d find |
He tried his best to solve the problem, _____ difficult it was.
| A．however | B．no matter | C．whatever | D．although |
The missing boy was last seen_____ near the East Lake.
| A．playing | B．play | C．played | D．to play |
Out of ___ for the homeless children he gave them shelter for the night.
| A．shock | B．shame | C．sympathy | D．surprise |
The _____house smells as if it hasn’t been lived in for years.
| A．little white wooden | B．little wooden white |
| C．whit wooden little | D．wooden white little |