79. Before there goes the bell for class, our math teacher took out a piece of       and wrote his problems on the blackboard.

A．brush pen

B．chalk

C．paper

D．Pencil

血痕的确证试验阳性结果表明检材（）。

A、肯定含有血；

B、可能含有血；

C、含有人血；

D、含有动物血。