I'd be down!

I can see why you thought D was correct, I was initially tripped up on it too :) But simplifying the stimulus:

After the earthquake, Cali students dreamed about earthquakes. In this same time, no Ontario peeps dreamed about earthquakes. The author then claim experiencing earthquake make you dream about it.

Does knowing how many times they were dreaming help you? If Cali students dream once a week, and that dream involve an earthquake, vs Ontario students dreaming 7 times a week ... you don't get any useful observations! The main point is still that Ontario students didn't dream about earthquakes!

I read A as the only correct answer, because it's saying both groups were the same before the earthquake, then the earthquake happened, and we saw a change in the California group! I hope this helps, and if you're curious - this is the exact same methodology as a quasi-experimental study! Hit me up if that piqued your interest haha.