[单项选择]The most versatile ______ embryonic stem cells, which ______ found in the embryo at the earliest stage of development and can grow into any part of the body.
A. are, are
B. is, is
C. are, is
D. is, are

[单项选择]With the technology of freezing stem cells from different strains of chicken, ______.


A. chicken farmers can order certain strains of chicken for economic reasons
B. origen can hardly supply all the strains of chicken the market might need
C. chicken farmers can order certain strains of chicken only
D. origen can be supplied with whatever strain they need

[单项选择]When stem cells specialize, they ______ .
A. grow into body parts
B. are destroyed
C. are set back to a pristine state
D. turn nose into kidney

[单项选择]The time of day when you feel most energetic is when your eyele of body temperature is at its peak.


A. 有一天当你感觉精力最充沛的时候，你的体温正处于高峰期。
B. 一天内你感觉精力最充沛的时刻，是你的体温循环周期处于高峰的时刻。
C. 一天中当你感到最有精力的时候，是你的体温循环最快的时候。
D. 当你的体温循环最快的时候，新的一天开始了。

[单项选择]

Time spent in a bookshop can be most enjoyable, whether you are a book-lover or merely there to buy a book as a present. You may even have entered the shop just to find shelter from a sudden shower.Whatever the reason, you can soon become totally unaware of your surroundings. You soon bury yourself in some book or other, and usually it is only much later that you realize you have spent too much time there and must dash off to keep some forgotten appointment.
This opportunity to escape the realities of everyday life is the main attraction of a book shop. A music shop is very much like a bookshop. You can wander round such places to your heart’s content. If it is a good shop, no assistant will approach you with the greeting, "Can I help you" You needn’t buy anything you don’t want. In a bookshop an assistant should remain in the background until you have finished browsing (浏览). Then, and only then, are his services necessary.
On
A. blamed
B. educated
C. welcomed
D. advised