Doubling which quantity would cause the largest increase in a spring's elastic potential energy?

displacement

spring constant

mass

gravitational acceleration

The answer is probably gravitational acceleration.

If the mass increases, and everything else remains the same, Newton's Second Law says theacceleration must de crease. The mass will move more slowly. If it moves more slowly, it will require more time to go through one period

I said gravitational acceleration but it was marked incorrect. I think the answer might be spring constant.