Explanation:
I think your answer is D, and let me explain why.
Heat can denature proteins quickly because proteins have very specific temperatures at which they act best. If the temperature rises too high/falls too low with respect to that threshold, then that will cause the proteins to stop working properly and eventually die.
pH is also very important with how proteins work, and it's the same reason as heat. Proteins have a certain range of pH's that keep them healthy and working, but as soon as the pH changes dramatically outside of that range, the proteins will be quickly denatured.
And lastly, organic solvents can denature proteins as well (e.g. alcohol), which makes sense because they are solvents (a solvent is something that dissolves other substances). I'm not sure about the exact chemistry / biological responses behind it, but it's what would be expected of a solvent.
With all of this in mind, I think your answer should be D!
