In the contract, usually there is a ________ clause to protect the buyer against loss from delay of the shipment of the goods.

A．payment

B．shipment

C．penalty

D．quality

 某高层建筑耐火等级为一级，1~3层为商业营业厅，每层面积为9800m²，采用不燃材料装修；地下一层为汽车库，面积9800m²。设有火灾自动报警系统，自动喷水灭火系统、消火栓系统等系统。

商业营业厅每层至少应划为（）防火分区。

A.3个

B.4个

C.5个

D.6个