The answer is the fourth one (d): active site, substrates, products.
Explanation for each option:
a. Active site, intermediates, products: This option is partially correct. Enzymes do have an active site, and they convert substrates into products. However, the term "intermediates" is not typically used in this context to describe what binds to the active site.
b. Proteins, substrates, vitamins: This option is incorrect. While enzymes are proteins, the statement does not correctly describe the process of enzyme action. Enzymes bind to substrates, not vitamins, to convert them into products.
c. Substrate, active sites, products: This option is incorrect. It incorrectly suggests that substrates have active sites, which is not the case. Enzymes have active sites that bind to substrates.
d. Active site, substrates, products: This option is correct. Enzymes have an active site that binds to substrates and converts them into products. This accurately describes the function and process of enzyme activity.
In summary, the correct answer is (d): active site, substrates, products.