A:when; which
B:that; which
C:which; that
D:when; that
若a、b互为相反数,c、d互为倒数,m的绝对值是3,求a+b5+3m-cd的值.
若直线l1,l2的方向向量分别为a→=(2,4,﹣4),b→=(﹣6,9,6),则( )
如图所示,AB∥EF∥CD,∠ABC=90°,AB=DC,那么图中的全等三角形有( )