钢材做成“V”形是因为材料的抗弯曲能力与其形状____关。
They ________ carefully, but they didn't ________ anything.
如图所示，灯L标有“2.5V 1.25W”字样，R1=15Ω，滑动变阻器R2最大阻值为10Ω，当开关S1闭合，S2、S3断开，滑片P滑至左端时，灯L恰好正常发光．试求：
