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【单选题】
妊娠囊内见到胚芽和有节律的胎心搏动一般为
A.
妊娠第6周到第7周
B.
妊娠第7周到第8周
C.
妊娠第8周到第9周
D.
妊娠第9周到第10周
参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Biological ClockWhen the sun rises on a warm and sunny day, you can see some flowers open up. When they close late in the afternoon, other flowers open.Biological rhythms（生物节律）, like the opening and c...
A.
But where can you find it?
B.
This makes them feel tired.
C.
In the summer they fly back to have babies.
D.
We are learning more and more about them.
E.
Biological clocks can be adjusted.
F.
Other rhythms are based on months, seasons or years.