Before I got to the cinema, the film()
A. had begun
B. has begun
C. is begu
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超声波检验方法适用于:厚度为()的碳钢支管坡口焊缝和角焊缝。
A. ≤10mm
B. ≥10mm
C. ≤5mm
D. ≥5mm
多普勒天气雷达使用低脉冲重复频率PRF测(),用高脉冲重复频率PRF测()。
非辐射专业人员或(),不得擅自对放射源进行操作,以免造成不必要伤害。
When talking to people within your company don’t speak your language, you may have to use English.()
A. who
B. which
C. whose