试题题干
Fill in the blanks with an item as required.
With a relative pronoun:
Ultrasonic sounds produce pulse signals, by means of
various defects in metal can be detected.
参考答案
试题解析
本题考查定语从句。由题干逗号可知是非限定性定语从句，且放在介词of后面，所以用关系代词which。
句意：超声波产生脉冲信号，通过脉冲信号可以检测出金属中的各种缺陷。