I belienve the answer is a or c... hope it helps
Formal research is usually done in an academic or professional setting like a physics institute or a university school of medicine
Informal research is done by individuals (like authors and inventors studying the background [“prior art”/“state of art”] of their respective areas of inquiry).
Vending machines, because each is just a word telling you that both were empty. Vending machines is what the whole sentence is based on.
Answer:
The school was closed because of strike.
Explanation:
Mostly by selling liquor and probably other illegal things
