About the definition of the word “study”

The problem with the question is when it uses the definite article: "What is the definition..." Very few words have only one definition. The question doesn't specify the part of speech. Answer 4 is appropriate if study is a noun. And yes, answer 3 is absolutely true if it's a verb. And there are many other possible definitions (e.g. a room dedicated to reading and writing).

This is one of the many times that a test or other teaching resource offers a right answer when there are in fact other possible right answers. (It's a particular problem when the multiple-choice offerings include one of the other possible right answers, without acknowledging it.)