Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Gabbro is a dark dense rock that can be found in the oceanic crust.
Gabbro is a dark dense rock that can be found in what?

Protons and neutrons are made of quarks, which are fundamental particles of matter.
A fundamental particle of matter, protons and neutrons are made of these?

Alternative current is produced when a magnet or coil moves back and forth repeatedly.

Alternative current is produced when a magnet or coil does what?