Answer:
Option D is the last answer.
Step-by-step explanation:
The main idea in a text refers to the most important one; also, the text is build around it with other supporting details or supportive ideas, which are intended to reinforce the main one. In this case, the one that has the lowest amount of contribution to the main idea (which refers to Carol and her research) is Carol has a cottage near the shore because it doesn't really affect the fact that she studies marine life.