For the purpose of training and drills，if reasonable and practicable，rescue boats on an OSV must be launched with their assigned crew（）.

A.once a week

B.once a month

C.once a year

D.twice a year

司可巴比妥溶液的澄清度检查物质是（）

A．苯丙二酰脲

B．酸性杂质

C．2-苯基丁酰胺

D．对氨基酚

E．苯基丁酰脲