Question

In which respect is a secondary source more helpful than a primary source?

Answer 1

I am pretty sure that secondary source more is more helpful than a primary source in hte way : C. A secondary source summarizes large amounts of evidence. Definitely, even though both primary and secondary source are the most essential points in the essay, secondary embraces more information by making conclusions connected to all the paragraphs. 
Do hope it will help you!

Answer 2

C. A secondary source summarizes large amounts of evidence.