成人胃管插入的深度为 __________ cm。
参考答案:45~55
动物园新建一座动物游泳池,它的周长是70米,长和宽的比是4:3。它的面积是多少平方米?
You ___ do it even if you don't want to. [ ]
A. can't
B. mustn't
C. have to
D.needn't