若两条直线ax+2y+6=0与x+(a﹣1)y+(a2﹣1)=0平行,则a的取值集合是( )
A:{﹣1,2}
B:{﹣1}
C:{2}
D:23
一 Long time no see!
— I've just retuned. I to Zhengzhou for a meeting last month.
用酵母菌使葡萄汁产生葡萄酒,当酒精含量达到12%~16%时,发酵就停止了.有关叙述不正确的是( )