The most appropriate antonym for the underlined word “intensify” is Option B. 

In this context, “intensify” means to become more intense or to increase in degree or extent. Therefore, the opposite of “intensify” would be to decrease or lessen, which is what “diminish” means. The other options, “amplify” and “escalate”, are synonyms of “intensify”, not antonyms, and “vorsen” is not a recognized English word. 

Therefore, “diminish” is the correct choice.