This confused me. high temperatures cause the enzyme to and have its structure start to break up. a: denature b: remain the same c: activate d: unravel

The answer is A, denature.

As each type of enzymes has its own optimum temperature, like the temperature that they work fastest at, so if the temperature goes too high above the optimum, the 3D structure of the enzyme breaks apart and deforms and they can no longer bind with substrates thus no longer works. In this scenario, we say the enzyme is denatured.

Note that only if the temperature is too high can make the enzyme denature, if the temperature is too low, instead, the enzyme would be inactive, but once the temperature goes back to normal, they work again. Unlike denatured enzymes, which does not work even if the temperature goes back to normal.