简述螺杆冷却的目的和意义。
参考答案:
①利于物料输送;②防止塑料分解;③利于气体排出;④均化段螺深变浅,利于塑化均匀;⑤避免温升造成挤出压力波动;⑥使温度控制在工艺要求内。
The man took out his iPad and saw the latest film while his car _____.
A.had been repaired
B.had repaired
C.was being repaired
D.was repairing
金属导体的电阻与()有关。
A.导体长度
B.导体截面积
C.外加电压
D.导体电阻率