如果古潜山上边的披覆层是（）层，古潜山就形成了储集油气的圈闭。

A、砂岩

B、剥蚀面

C、渗透

D、非渗透

The irrevocable L/C can（）.

A．be amended or canceled without notice to the beneficiary

B．be amended or canceled if the buyer notifies the seller

C．neither be amended nor canceled without agreement of all parties

D．be amended but not be canceled by an applicant