流动资金是指为维持生产所占用的全部周转资金，它是( )。
A. 现金与银行存款的总和
B. 全部货币资金
C. 流动资产与流动负债的差额
D. 资产与负债的差额
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After the right time for learning a language has passed, ______.
A. you can only learn to write and read it
B. you can hardly learn to speak it as well as a native
C. you cannot detect the subtle differences between sounds
D. you cannot work tongue, throat, and lips to control breathing
Soon after the drug ______ effect, the patient became quieter.
A. brought
B. made
C. took
D. released
Motion pictures ______.
A. cause inertia of the eye
B. show a succession of unrelated movement
C. show consecutive phases of movement which appear continuous
D. show each phase of movement for one-half of a second
A picture remains on the retina for ______.
A. 6 seconds
B. second
C. 16 seconds
D. 1/6 of a second
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