清朝雍正年间，市面流通的铸币，其金属构成是铜六铅四，即六成为铜，四成为铅。不少商人出以利计，纷纷熔币取铜，使得市面的铸币严重匮乏，不少地方出现以物易物。但朝廷征于市民的赋税，须以铸币缴纳，不得代以实物或银子。市民只得以银子向官吏购兑铸币用以纳税，不少官吏因此大发了一笔。这种情况，雍正之前的明清两朝历代从未出现过。从以上陈述，可推出以下哪项结论I．上述铸币中所含铜的价值要高于该铸币的面值。II．上述用银子购兑铸币的交易中，不少并不按朝廷规定的比价成交。III．雍正以前明清两朝历代，铸币的铜含量，均在六成以下。
A．只有I。
B．只有II。
C．只有IⅡ。
D．只有I和II。
参考答案：C
解析：诸选项中，B和C项都能削弱题干的结论，但是，B项是说立氏化妆品的广告几乎没有影响，c项是说立氏化妆品的广告有负影响，即起了负促销作用。显然，C项比B项更能削弱题干。其余各项均不能削弱题干。
Electronic books have changed the way many people read for 15 . Now online textbooks are changing the way some students learn and some teachers teach. More than 16 students go to the public schools in Fairfax County, Virginia, outside Washington. Last year, the school system used digital books in fifteen schools. This school year, middle schools and high schools changed 17 printed to electronic textbooks in their social studies classes. “I mean, it’s just 18 a regular textbook, except it’s got it all online.” says Luke Rosa, a history teacher at Falls Church High School. Peter Noonan, an assistant superintendent(主管) of schools says, “The world’s changing 19 . And the online textbooks can change right along with the events that 20 .” “Digital books also cost 21 than printed textbooks,” he says, “Usually it’s between fifty and seventy dollars 22 a textbook for each student, which adds up to about eight million dollars for all of our students in Fairfax County. In fact, we have bought all of the online textbooks for our students for just under six million dollars.” Social studies teacher Michael Bambara says the e-book he uses in his government class is better than a(an) 23 textbook. It has materials for students 24 different levels of reading skills…
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