In order for a massive star to form a black hole, it must first
a. expand
b. emit x-rays
c. run out of fuel
d. begin rotating faster

Kelly ran electricity though a sample of water using electrolysis. the water changed into two gases, x and y. it was not possible to break down the gases x and y into simpler particles.

What occurs to the cell during mitosis

For a comparative or experimental investigation, scientists often make a testable about a scientific question, and then they test it in the investigation. a.control b.hypothesis c.procedure d.system