Question

If the quadrilateral formed by the lines ax+by+c=0,a′x+b′y+c=0,ax+by+c′=0,a′x+b′y+c′=0 have perpendicular diagonals, then

Answer 1

Which of the following is a subordinate clause?

We need to leaveAlex was lateNatalie and Denise ate lunchBy the time they arrived