为什么到现在为止还没有得到在所有温度下都缺乏5'→3'的外切酶活性的DNA聚合酶Ⅰ的突变株？
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A. at random
B. in brief
C. on purpose
D. so far
Bob：Fine．It never rained during my stay here．
A. How about the weather
B. How is the weather
C. What is the weather
D. What do you think of the weather
表2-5
测得水样中BaP以高度表示的吸光度为0.862 mAU。在同一水样中加入20μL BaP标准溶液(20mg/L)，加标后测得试样的Height(mAU)=6.584。试计算水样中BaP的含量和实验的加标回收率(水样总体积1mL，不考虑加标体积变化)。
Wearing a seat belt in a vehicle （).
A. reduces road accidents by more than half
B. saves lives while driving at a speed up t0 30 miles per hour
C. reduces the death rate in traffic accidents
D. saves more than 15000 lives each year
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