I _____while my friend _____ TV.[ ]

A. arrived; was watching

B. was arriving; watched

C. arrived; watched

D. was arriving; was watching

急性CO中毒的主要机制是（）

A.与含二价铁的肌球蛋白结合，损害线粒体功能

B.与红细胞的Hb结合，形成HbCO，引起组织缺氧

C.抑制细胞色素氧化酶的活性

D.产生高铁血红蛋白

E.影响呼吸链的电子传递