Answer:
The researcher should measure the difference in the amount of product at the end of the reaction.
Explanation:
Enzymes are defined as the protiens that are responsible for increasing the rate of reaction.
With the increase in temperature, the enzyme activity increases and so the rate of reaction increases. It means at lower temperature the rate of reaction decreases and the amount of product also decreases.
So, to determine the effectiveness of an enzyme at various temperatures, the difference in the amount of the product at the end of reaction should be measured.
Hence, the correct answer is "D".