额定电压为U₀的电灯，其均匀灯丝常温下的电阻为R，下列说法中正确的是

A．常温下，若将灯丝均匀拉长为原来的10倍，则电阻变为10R

B．常温下，若将灯丝从中点对折起来，电阻变为

C．给灯丝加上从0到U₀逐渐增大的电压，其比值不变

D．将灯丝温度降低到接近绝对零度时其电阻会突变为0

Limit switches on gravity davits should be tested by（）.

A.the engineers，from a panel in the engine room

B.shutting off the current to the winch

C.pushing the switch lever arm while the winch is running

D.All of the above