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
