A student proposes this hypothesis in class: "If I make the angle of a ramp steeper, then a ball rolling down the ramp will be going faster when it hits the ground.”

Which part of a hypothesis should the student add to this that could also be tested in other experiments?

an explanation based on prior scientific knowledge or observations
an explanation of how the hypothesis will inspire new questions
an independent variable that the student controls during the experiment
an independent variable that is affected by the other experimental variable