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【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.
【单选题】解决物的不安全状态的途径可通过（）来进行。
A.
培训提高人的安全意识和安全能力
B.
系统论的方法改善组织的结构
C.
各种有效的安全技术系统保证安全设施的可靠性
D.
建立有效程序和报告制度