What I gather from the questions and answers is that the receiving antenna is located to the north of the transmitter, and it is also oriented to point north/south. This is totally not clear from the passage. The real MCAT would have done a better job describing the antenna layout.
For question 50, the passage says the transmitting antenna is oriented vertically. The passage says the electric field of the propagating wave will be oriented the same as the antenna. So the electric field will be oriented up/down. This was a fair question.
For question 47, the passage says the electric field (up/down) creates a current in the receiving antenna. Thus if the receiving antenna is in the same orientation (up/down) then the current created will be at a maximum because it can slosh those electrons up and down the whole length of the antenna. However I think this is really glossed over in the passage - it is borderline relying on prior knowledge. The real MCAT wouldn't do this. A real MCAT question would be more easily answered by the passage.
For question 52, the passage says that magnetic field will be perpendicular to the electric field (up/down). It also says the magnetic field will be perpendicular to the direction of travel (north, because the receiving antenna is apparently to the north). Therefore the magnetic field must be oriented east/west. Again, the real MCAT would have done a better job of describing the antenna positioning.
OP, if you were lost because you don't really understand electromagnetic waves, your best bet would be to review that chapter in your physics book. It's an important topic for the MCAT, and a little hard to teach in just a forum post. This passage should have been 90% review material, and question 50 should have been a gimme. Questions 47 and 52 were not really MCAT worthy based on the passage you posted.