聚合反应的步骤（）。
A.链引发
B.链增长
C.链终止
参考答案：A, B, C
He________ six symphonies by the time he was 20.[ ]
A. wrote
B. has written
C. had written
D. writes
熔体管道的加热介质可以是（）。
A.三甘醇
B.氢化三联苯
C.联苯-联苯醚
D.对二甲苯
