机织用的经纱捻系数应大些,以保证强力。
参考答案:对
It _____ me two and a half hours _____ my homework yesterday.[ ]
A. took; to do
B. takes; to do
C. spent; doing
D. cost; to do
负载连接导线和开关称为()。
A、内电路
B、电路
C、外电路
D、串联电路