蛋白质工程的实质是[ ]

A．改造蛋白质

B．改造mRNA

C．改造基因

D．改造氨基酸

There are some boys on the playground. They _____ football.

They _____ a football match next Saturday. [ ]

A. play; have

B. are playing; are going to have

C. play; are having

D.are playing; have