题目

Imitating others' actions in Tik Tok _____ be very dangerous, so you can't be too careful. A . should B . shall C . might D . can 答案：D18．已知函数$f（x）=\sqrt{\frac{x+1}{x-2}}$的定义域是集合A，函数$g（x）=\frac{1}{{\sqrt{{x^2}-（2a+1）x+{a^2}+a}}}$的定义域是集合B．（1）求A，B（2）若A∪B=B，求实数a的取值范围．