For this question, choose the option opposite in meaning to the word or phrase in italics.  The manager became flexible on critical matters.

Step 1: Analyze the question We need the word opposite in meaning (antonym) to "flexible" in the sentence: "The manager became flexible on critical matters."

Step 2: Explain the concept "Flexible" means willing to change or adapt, or able to bend easily without breaking. Its antonym describes something that does not change or bend, i.e. stiff and inflexible.

Step 3: Check each option

• A. rigid: means stiff, fixed, not willing to change. This is the direct opposite of flexible.
• B. unbendable: this also means not able to bend, so it looks like an antonym too. However, it is a literal, physical description (an unbendable rod) and is rarely used for a person's attitude. It is also essentially a synonym of "rigid", so it could not be the single best answer when "rigid" is offered.
• C. evasive: means avoiding answering or committing. It is not the opposite of flexible.
• D. serious: means grave or earnest. It has no relationship to flexibility.

Step 4: Decide Both A and B carry the sense of "not bending", but "rigid" is the standard, most natural antonym of "flexible" in English usage, and it fits the figurative meaning in the sentence (a manager who is unwilling to change their position).

Answer: A. rigid

Tip: In antonym questions, when two options seem similar, pick the one that is the most common, standard opposite and fits the context (here, a person's attitude). Also remember the pair: flexible ↔ rigid, lenient ↔ strict.