If the suffix -ate means “cause to become,” what does captivate mean?
a. cause to become made
b. cause to become seen
c. cause to become stretched
d. cause to become taken

The answer is: [D]: cause to become taken.

Explanation: Given: "the suffix -ate means 'cause to become' ; 
 the remaining "root" of the word: "captivate"— is: "captiv-" ;
           which is similar to: "captive".

Since all answer choices given begin with: "cause to become"; it makes sense that "cause to become taken"—which is "Answer choice [D]"; is the most appropriate—and thus the correct—answer.
"captive".