Final answer:
Temperature is the variable likely affecting enzyme function in the given scenario as it can cause enzymes to denature outside of their optimal range, similarly pH levels can also affect enzymes but was not chosen here.
Step-by-step explanation:
Enzymes, as proteins, have specific conditions under which they function optimally. Given the options provided, the variable affecting enzyme function is most likely temperature. Enzymes have an optimal temperature range and deviating from this range can affect the enzyme's ability to bind substrates due to changes in the active site's chemical bonds. High temperatures can lead to denaturation, where the enzyme loses its three-dimensional structure and its functionality. Similarly, enzymes are sensitive to pH levels as the active-site amino acids require specific acidic or basic conditions to catalyze reactions effectively. Extreme pH levels can also cause denaturation. Therefore, factors like temperature and pH play critical roles in enzyme activity.