What information do you learn about the author that establishes him as an authority on this topic？
A. He has suffered a lot in losing his privacy.
B. He makes his living off of the Web.
C. He knows how to monitor his account.
D. He and his wife published a book concerning computer hackers.
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已知消费者的收入是100元，商品X的价格是10元，商品Y的价格是3元，假定他打算购买7单位X，10单位Y，这时商品X和Y的边际效用是50和18，想获得最大效用，他应该()。
A. 停止购买
B. 增加X，减少Y
C. 增加Y，减少X
D. 同时增购X和Y
Which of the following is true to Wikipedia？
A. More than 4,000 pages are offered for edition.
B. More than 2,400 Wikipedians work for the edition.
C. Everyone can do the revision on the web page.
D. The entries contribute to people's development.
王某与李某协商，将王某的私房卖给李某，二人之间的买卖行为可以书面形式进行，也可以口头形式完成。()
A. 正确
B. 错误
He was reluctant but he______ because he wanted to find out more about their plans before
A. played along
B. played down
C. played about
D. play in
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