Unit13 We’re trying to save the earth!SectionB(1a-2f)I. 单项选择:(BC 层学生必做,A 层选做或不做)( )1.----This is really__________ ugly bird. ----But it is _________useful bird. It can help fishermen catch fish.A.an;aB.an;anC.a;aD.a;an( )2. ----Why haven't you bought a car,Mr.Lin? You can __...