电梯钢丝绳或链条最少应有两根，每根钢丝绳或链条应是独立的。（）
参考答案：对
______ you think he ______ back by dinner time?
a. Do/have come b. Did/will have come c. Does/will come d. Do/will have come
一块长方形的钢板长18米，宽10米，这种钢板每平方米重45kg，这块钢板有多重？
