函数y=lg(x2+3kx+k2+5)的值域为R,则k的取值范围是( )。
(-∞,-2]∪[2,+∞)
If you ________ Beijing Duck,I'd like to treat you to a meal at a famous duck restaurant.
A.didn't try
B.don't try
C.haven't tried
D.hadn't tried
基因工程