超声波探伤，为减少近场长度应选用低频率或晶片直径较小的探头。
参考答案：对
Perhaps the best sign of _____ computer and internet use pushes up demand for paper comes from the high-tech industry itself.
A．how
B．what
C．why
D．that
能够造成婴儿视网膜病变的是（）.
A．四环素
B．反应停
C．氯霉素
D．新生霉素
E．磺胺
