假设企业客户流失率为20%，那么客户群体的生命周期为5年(1/20%)。()
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By writing Paragraph 1, the author intends to______.
A. advocate that pet animals do as well have traits
B. prove that little attention has been paid to the personalities of animals
C. introduce a study focusing on birds" behaviors
D. state that people differ from animals because of personalities
企业收到请求后，通过电话、邮件、上门等方式提供服务属于主动服务。()
The Visx machine determines how accurately the eye______.
A. can see distance
B. is able to read eye charts
C. bends the light
D. is working
The authors attitude towards the Visx machine is that______.
A. it is interesting but not very useful
B. he says it"s a wonderful invention which could replace eye charts
C. it can be useful but he thinks it"s too early to make a switch
D. too much time and money have been wasted on it
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