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【多选题】
可见分光光波度法中,当测得待测物质溶液的吸光度不在0.7~0.2范围时,为了减小浓度测量的相对误差,可以A.
读数太大时,将溶液准确稀释再测定
B.
读数太小时,改用较厚的比色皿
C.
改变测定的波长,选用波长较短的光波
D.
更换光源
E.
读数太大时,改用较薄的比色皿
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【单选题】Americans are getting ready for the biggest soccer event in the world. For the first time the World Cup soccer competition will be held in the United States. While millions play the game around the wo...
A.
Americans were preparing for the World Cup when the author wrote this article.
B.
More and more young Americans became interested in soccer in the last 30 years.
C.
Soccer is the fastest developing sport in the world.
D.
The article was written before the World Cup held in the United States.
【简答题】For the first time in history, more people live in towns than in the county. In Britain this has had a curious result. While polls show Britons rate “the countryside” alongside the royal firmly, Shake...
【简答题】（1）已知 tanα= 2 3 ， 1 sin 2 α-2sinαcosα+4 cos 2 α 的值． （2）已知 π 4 ＜α＜ 3π 4 ，0＜β＜ π 4 ，且cos（ π 4 -α）= 3 5 ，sin（ π 4 +β）= 5 13 ，求sin（α+β）的值．
【单选题】When did the Chinese create paper money for the first time in the human history? And when did the Chinese government print recognizable paper money for the first time in the human history?
A.
900s and 916
B.
1100s and 1024
C.
1500s and 1511
D.
1570s and 1581
【单选题】Women are on the verge of outnumbering men in the workforce for the first time, a historic reversal caused by long-term changes in womens roles and massive job losses for men during this recession. Wo...
A.
Men make up the most profitable sectors.
B.
Women gain jobs while men lose jobs.
C.
Women take the most jobs in the economy.
D.
Women outnumber men in few sectors.
【简答题】已知cosα-sinα= 3 5 2 ，且π＜α＜ 3 2 π，求 sin2α+2cos2α 1-tanα 的值．
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