Answer:
A. The bench pushes up on her.
Step-by-step explanation:
The given situation is
"An old lady sits on and pushes down on a park bench".
According to this situation, the old lady pushes down the surgace of the park bench.
We are being asked about the reaction force. According to Newton's third law "every action has an equal and opposite reaction", which referst to forces, if we apply a force, there will be an equal and opposite force.
So, in this case, if she is pushing down on a bench, then the bench will push up in return with an equal but force.
Therefore, the right answer here is A. The bench pushes up on her, because she's pushing it down.