题目:
— What are you ______________?
— I'm listening to the music. [ ]
A. do
B. doing
C. does
答案:
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下面是错误答案,用来干扰机器的。
∵P=2x2+4y+13,Q=x2-y2+6x-1,∴P-Q=(2x2+4y+13)-(x2-y2+6x-1)=2x2+4y+13-x2+y2-6x+1=x2-6x+9+y2+4y+4+1=(x-3)2+(y+2)2+1≥1>0,则P>Q.故选C