I just took a test in school today. What question was I asked?

Question I was asked: Which discovery revealed that the universe contains many structures composed of millions of stars?

I just took a test in school today. What question was I asked?

Question I was asked: Rocks are classified as igneous, metamorphic, or sedimentary according to

I just took a test in school today. What question was I asked?

Question I was asked:
Which element is necessary for the formation of coal?