2) Professor Waters comes from ___________.
A) the United States
B) Canada
C) Australia
D) England
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3) Professor Waters____________.
A) knows well how to teach English
B) is a new hand in writing books
C) writes books in different fields
D) is very good at speaking English
4) This speech is a (an) ____________ speech.
A) thank-you
B) opening
C) welcome
D) closing
除二羟基丙酮外，单糖均为还原糖。
A. 对
B. 错
连通无向图G有6个顶点9条边，从G中删去（ ）条边才有可能得到G的一棵生成树T．
A. 3
B. 4
C. 5
D. 6
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