---Excuse me. Could you tell me              ?

---＄328.

A．how much is the ticket

B．how much does the ticket cost

C．what the price of the ticket is

D．how much should I pay for the ticket

张某是某施工单位的材料采购员，一直代理本单位与甲建材公司的材料采购业务。后张某被单位开除，但甲公司并不知情。张某用盖有原单位公章的空白合同书与甲公司签订材料采购合同，则该合同为( )。

A．效力待定合同
B．无效合同
C．可撤销合同
D．有效合同