Answer:
I have seen her at the pet shop before, but today I saw her at the gym.
Hope this helps, if It wasn't clear the answer is C) Saw
Reason:
The word "seen" was used earlier in the sentence so we can eliminate it, it also wouldn't make sense. The word "Sees" applies to me saying "Noah sees her at the gym" but that's not how the sentance went. And sawed would be cutting her in half at the gym so lets not do that.
Cheers
Noah