单选题 下列4条直线:l1:2x-3y+5=0;l2:3x-2y+1=0;l3:3xsinα-2ysinα+7=0.l4: .其中与直线2x+3y-10=0垂直的是( ).
l1,l2
l2,l3
l1,l2,l4
l3,l4
单选题 _____ our great surprise, our company has made much more profit than we expected last year.
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单选题 You can ask these experts _____ advice in job hunting.
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单选题 When I first arrived in Japan, I was surprised _____ the way people greeted each other.
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单选题 方程ax+by+c=0与方程2ax+2by+c+1=0表示两条平行直线的充要条件是( ).
ab>0,且c≠1
ab<0,且c≠1
a2+b2≠0,且c≠1
a=b=c=2
单选题 若O为坐标原点,过点P(rcosα,rsinα)(r≠0),且垂直于OP的直线方程为( ).
ycosα+xsinα+r=0
ysinα+xcosα+r=0
ysinα-xcosα-r=0
ysinα+xcosα-r=0