The storm caused severe damage（）
A. physical
B. accidental
C. serious
D. enviromental
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A new system of quality control was brought in to overcome the defects in the firm's products.
A. invested
B. introduced
C. installed
D. insisted
But from the start of their experiments, the Wright brothers found that they needed money to pay () their research.
A. back
B. down
C. for
D. off
mRNA上的四种核苷酸能组成多少种密码子
A. 4
B. 16
C. 61
D. 64
E. 81
美洲箭毒作为肌肉松弛剂是由于
A. 它和乙酰胆碱竞争终板膜上的受体
B. 它增加接头前膜对Mg2+的通透性
C. 抑制Ca2+进入接头前膜
D. 抑制囊泡移向接头前膜
E. 抑制终板膜的离子通道开放
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