Which of the following is a tip for effectively using presentation aids?
Always pass around presentation aids so your audience can view them up close.
B. If something happens to your aid, there’s no reason to keep going.
C. Every slide, graphic, and word on a computer presentation should be animated.
D. Aids need to be large enough to be seen by your entire audience.
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含有0.1250g I2的KI溶液25mL，用25 mL CCl4与之仪器振荡。I2在CCl4和KI溶液之间的分配达到平衡后，在水相中测得0.0050g I2，若每次用25mL CCl4萃取25mL该溶液，共萃取两次，萃取率是 （ ）
A. 86.0%
B. 96.0%
C. 99.0%
D. 99.8%
Fe3+在某有机相与水相的分配比是99，今有含10mg Fe3+的水溶液，若用等体积该有机溶剂萃取两次，则水相中剩余Fe3+的质量是 （ ）
A. 0.03mg
B. 0.01mg
C. 0.003mg
D. 0.001mg
水溶液中的Ni2+之所以能被丁二酮肟-CHCl3萃取，是因为在萃取过程中发生了下述何种变化？（ ）
A. Ni2+形成了离子缔合物
B. 溶液酸度降低了
C. Ni2+形成的产物的质量增大了
D. Ni2+形成的产物中引入了疏水基团
含Fe3+的HCl溶液，用3倍体积的含HCl的乙醚溶液萃取，已知Fe3+有99%被萃取，则分配比约为（ ）
A. 3.3
B. 33
C. 300
D. 30
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