During college I took the first chance I had to do field research, which I spent a summer studying marsh birds in Michigan.
A) same
B)spending
C)where I spent
THe answer is B but I can’t fully explain why.
I don’t want to get too technical with the grammar (though I can if you are not satisfied with the explanation), but basically both the which and the where make it seem as though they are referring to the field research (as in the field research spent a summer studying marsh birds in Michigan or that the field research is where I spent a summer…). The “spending” makes it seem like it is explaining the experience doing field research, which is the correct, logical meaning. Its technically a modifier question (and if you want to get really technical it is the difference between relative clauses and participial phrases), but I think you could also just look at it as a “meaning” question and probably see that the right answer is right because it provides the correct logical meaning whereas the other answers are either clearly illogical or at best confusing and ambiguous. Hope that helps!
“Which” rule: it must refer to the nearest noun or noun phrase. That doesn’t work here b/c you can’t say “I spent field research a summer studying marsh birds.”
“Where” rule: it must be a PLACE. No exceptions. That doesn’t work here because “field research” is an activity, not a place.