15. ---Do you know the girl in red?

---She seems to ______ me at last month’s party. But I’m not sure.

A．introduce to

B．be introducing

C．be introduced to

D．have been introduced to

如图，两个集气瓶中，上瓶装的是无色的空气，下瓶装的是红棕色的二氧化氮气体（二氧化氮的密度比空气大）．当抽出玻璃片后，短时间无法看到明显现象，如果下面用酒精灯加热，会观察到显著的现象：______．此现象说明______，当两瓶气体混合均匀后，分子______（填“继续”或“停止”）运动．