Which combination of conditions produces the highest density altitude at a given airport?

Explanation

Density altitude rises whenever the air becomes less dense, and heat, moisture, high elevation, and low pressure all thin the air, so a hot, humid day at a high-elevation site gives the highest density altitude. Water vapor is lighter than dry air, so high humidity lowers density rather than raising it. Cold air and high pressure both increase density, which lowers density altitude, so the remaining combinations all produce better performance.