A:红棕色的NO2加压后颜色先变深再变浅
B:H2、I2、HI混合气体加压后颜色变深
C:合成氨时采用循环操作,可提高原料的利用率
D:打开汽水瓶,看到有大量的气泡逸出
A:Hello,Tom.
B:Hi,Jenny. How do you feel?
A:I feel happy. Look! This is my sister(妹妹).
B:What's her name?
A:Her name is Kate.
B:What colour is her hair?
A:Her hair is black.
B:What colour are her eyes?
A:They are blue.
B:How nice(漂亮的)!
若x2+kx+4是一个完全平方式,则常数k的值为( )