Question

to understand the main idea of an informational text, you should ask yourself
\does the author include relevant details?\
\what is this mostly about?\
\which facts support the claim?\
\what evidence does the author provide?\

Explanation:

To find the main idea of an informational text, the key question is about what the text is mostly about. The other options are about details, supporting facts, or evidence, which are related to developing or analyzing the main idea but not identifying it directly. So the question "What is this mostly about?" is the one to ask for the main idea.

Answer:

B. "What is this mostly about?" (assuming the options are labeled A, B, C, D with B being this option)