The CPU does not have to look (66) all of RAM to find the spot it needs. But RAM only (67) the data temporarily. As soon as you switch the computer (68) , all that information disappears from the RAM. When you switch the computer on again, the RAM is (69) , and ready (70) a new program and new data.

（68）处填（）。

A．off

B．on

C．up

D．down

起挖大树时，土坨大小应比断根坨向外放宽（）cm，因新根在这一范围内发生较多。

A、10~20

B、20~30

C、30~40

D、40~50