Answer:
d. opinions
Explanation: To support evidence of a claim or counterclaim, an author needs to use facts, not opinions. An opinion could show that the author supports or doesn't support the claim, (Or counterclaim) but wouldn't use any evidence to say whether the claim is true or false.
Sub-questions are narrower questions. They are important because they provide the 'skeleton' around which you will find information to answer your main research question.