生产许可证产品必须进过（）合格才能出厂交付。
A.首件检验
B.巡回检验
C.完工检验
D.出厂检验
参考答案：D
人的感官察觉微弱刺激的能力称为（）。
A.绝对感觉阈限
B.绝对感受性
C.差别感受性
D.差别阈限
He studied very hard all the time because he didn’t want to __________in his studies.
A．fall behind
B．be left behind
C．left behind
D．Both A and B
