The correct answer is A. A man of no substance.
A man of straw is a man of no substance, a man who is not to be taken seriously. The phrase is often used to describe someone who is weak, cowardly, or easily manipulated.
Option B, a very active person, is incorrect. A man of straw is not necessarily active, but may be lazy or inactive.
Option C, a worthy fellow, is incorrect. A man of straw is not necessarily worthy, but may be unworthy or even despicable.
Option D, an unreasonable person, is incorrect. A man of straw is not necessarily unreasonable, but may be reasonable or even rational.
Option E, none of these, is incorrect. The phrase “a man of straw” is a well-known idiom with a specific meaning.