Step 1: Understanding the Concept:
This question asks for the antonym of the adjective REDOUBTABLE.
Step 2: Detailed Explanation:
Redoubtable means formidable, especially as an opponent. It describes someone or something that inspires fear, awe, or respect because of their strength, skill, or power.
The opposite would be someone or something that is not formidable and does not inspire fear or respect.
Let's analyze the options:
(A) Trustworthy means able to be relied on as honest or truthful.
(B) Unschooled means uneducated.
(C) Credulous means having or showing too great a readiness to believe things.
(D) Not formidable is the literal and precise opposite of redoubtable.
(E) Not certain means unsure.
Step 3: Final Answer:
The word redoubtable is a direct synonym for formidable. Therefore, its antonym is "not formidable." Option (D) is the correct answer.