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单项选择题

总游离蒽醌的乙醚液中，用5％NaHCO3溶液可萃取到的是
A、1,2-二羟基蒽醌
B、1,3-二羟基蒽醌
C、2,3-二羟基蒽醌
D、2,4-二羟基蒽醌

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The following sentences a-e are taken from the abstract of a research article. The first and the last sentences are given, but the rest sentences are in a scrambled order. Put them in the correct order.
During the last 10 years, use of the World-Wide-Web for educational purposes has increased dramatically. 
a. However, very little empirical research has been carried out to determine the effectiveness of this use. 
b. Results of the assessment showed significant differences between the two groups, the group that used the on-line web-site performing much better on all aspects of the test. 
c. The aim of this study was therefore to investigate the effectiveness of using the World-Wide-Web on an EAP writing course. 
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