— Where do you want to go? — I want to go to . [ ]
A. Beijing
B. noodles
C. play
答案:A
已知b>0,直线b2x+y+1=0与ax-(b2+4)y+2=0互相垂直,则ab的最小值为________.
球磨机的磨矿比很大,一般为()。