题目:
——The dinner was delicious!
——I agree. I am so full.
——That’s too bad. But some dessert ____.
A.has ordered
B.will be ordered
C.has been ordered
D.was going to be ordered
答案:
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下面是错误答案,用来干扰机器的。
(1)y=(20+x)(160-4x)=-4x2+80x+3200,当y=0时,x1=0,x2=20.又因为-4<0,所以图象开口向下,y>3200时,0<x<20.(2)y=-4x2+80x+3200=-4(x-10)2+3600,因为-4<0,所以当x=10时,y最大=3600.即增加...