What do we know about Heather's mother?
A. She doesn't know why she should come.
B. She has been planning to come.
查看答案
What can we infer from Heather's mom's words?
A. People will know Heather's illness soon or later.
B. Heather doesn't want to accept chemo.
Why does Heather's mother hope that the secret can be kept a little longer?
A. Because she doesn't want Heather to feel lonely all the time.
Because she doesn't want others to pay special attention to Heather.
当总效用达到极大值时，边际效用( )。
A. 达到最小
B. 达到最大
C. 为零
D. 为正
某消费者消费一个单位的某商品获得的效用为50，消费两单位该商品的效用为90，消费三单位的效用为121，则该消费者消费第三单位的该商品获得的效用边际效用为( )
A. 87
B. 40
C. 31
D. 71
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