English Idiom — Choose the correct meaning. Sentence: The class could not keep a straight face on hearing the strange pronunciation of the new teacher.

Introduction / Context:
“To keep a straight face” means to remain serious and avoid laughing or smiling, especially when something is unintentionally funny. In classroom anecdotes and workplace stories, this idiom describes the effort to maintain decorum despite comic provocation—in this case, unusual pronunciation by a new teacher.

Given Data / Assumptions:

• Trigger: “strange pronunciation.”
• Group: “the class,” implying social pressure to laugh.
• We must choose the meaning of the idiom, not literal facial posture only.

Concept / Approach:
The idiom focuses on seriousness vs amusement. Silence or muteness do not necessarily indicate seriousness; people can be silently amused. “Remain disturbed” refers to being upset, which is not implied. Therefore, “remain serious” is the exact interpretation of the idiom as used in the sentence.

Step-by-Step Solution:

Verification / Alternative check:
Paraphrase: “The class could not remain serious.” This captures the failure to suppress laughter, which is the point of the story.

Why Other Options Are Wrong:

• remain silent: Silence does not equal straight-faced seriousness.
• remain mute: Focuses on speechlessness, not facial expression.
• remain disturbed: Indicates anxiety or upset, not humor control.

Common Pitfalls:
Equating “not laughing aloud” with silence. The idiom specifically contrasts seriousness with the urge to laugh, not speaking vs silence.

Final Answer:
remain serious