A:蜜蜂、苍蝇
B:蜻蜓、蝴蝶
C:白蚁、狒狒
D:家蚕、蚊子
He was just falling asleep _____ there was a loud knock on the door.
先化简,再求值: x2+2x+1x+2÷x2−1x−1−1x+2 ,其中 x=2−2 .