His books are well known for their progressive ideas.

A. useless

B. old-fashioned

C. complex

D. reactionary

Answer: Option D

Solution(By Examveda Team)

Progressive : happening or developing gradually or in stages.
Useless : not fulfilling or not expected to achieve the intended purpose or desired outcome.
Old-fashioned : in or according to styles or types no longer current; not modern.
Complex : consisting of many different and connected parts.
Reactionary : opposing political or social progress or reform.

Antonym of Progressive is Reactionary