枣核式绳帽主要由绳帽体和钢球组成。
参考答案：错
The number of foreign students attending Chinese universities _____ rising steadily since 1990.
A．is
B．are
C．has been
D．have been
将一根导线均匀拉长为原长度的3倍，则它的阻值约为原阻值的（）。
A.3倍
B.6倍
C.4倍
D.9倍
