【C19】
A. which
B. there
C. where
D. that
Ships with crew are more costly mainly because of______.
A. pay and accommodation for sailors
B. hotel facilities needed on board
C. expenditure on more fuels
D. heating and plumbing
斯金纳认为学习的实质就是“反应概率上的一种变化”，这种变化可用操作性条件反射来解释。()
施工升降机附墙架安装尽可能保持水平，若有倾斜，其倾角一般最大允许为().
A. ±8°
B. ±6°
C. ±10°
D. ±12°
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