脉冲电泳用于核酸分离，其优点是分离大片段核酸，这种电泳的电场为（）

A.正交的脉冲电场

B.负交的脉冲电场

C.正交的交变脉冲电场

D.负交的交变脉冲电场

E.以上都是

During an annual FCC inspection（）.

A.all required documents and publications may have to be produced

B.licensed GMDSS radio operators may be required to demonstrate equipment competencies

C.all required equipment must be fully operational

D.All of the above