—Yang yan, are you coming with us?

—I’d love to, but something unexpected ______.

A．was coming up

B．had come up

C．would come up

D．has come up

在下列环境问题中，通过食物链引起危害的是 [ ]

A．酸雨

B．臭氧层空洞

C．温室效应

D．废电池的污染