A:will
B:shall
C:are going to
D:went
—______. We don't have enough money.
内燃机在做功冲程,高温气体迅速膨胀做功后,气体的温度和内能变化的情况( )
直线l1的倾斜角的正切值为-3,直线l2与l1垂直,则l2的斜率是( )