A positive test charge is placed at the origin. A charge +Q is fixed at (a,0) and a charge −2Q at (0,a). In which quadrant does the net electrostatic force on the test charge lie?
a) Third quadrant (−x,−y)
b) First quadrant (+x,+y)
c) Second quadrant (−x,+y)
d) Fourth quadrant (+x,−y)