The number of the teacher invited _____ twelve, but a number of them ___ late for different reasons.

A．were; was

B．was; was

C．was; were

D．were; were

特定之债与种类之债的划分依据是（）。

A．债的标的物的性质

B．债的内容是否特定

C．债权人是否特定

D．债务人是否特定