Select the meaning of the underlined idiom from the given options. The people…

Concept: An idiom is a fixed expression with a meaning that must be learned as a whole; it usually cannot be worked out from the literal meaning of its individual words. 'En masse' is an idiom (borrowed from French) used in English to describe an action carried out by many people together, all at once, as a single group.

Application: In the given sentence, the people marching en-masse against the new law means they marched together, as one collective group, rather than separately. This matches the meaning 'in a group'.

Cross-check: Checking the idiom's sense against each remaining option confirms none of them fit:

• 'Singly' describes acting alone, one person at a time — this describes individual action, not a shared collective action.

• 'Angrily' names an emotion; it says nothing about how many people were involved or whether they acted together.

• 'Loudly' describes the volume of sound produced, not who was involved or how they were organised.

Since 'en masse' specifically conveys a group of people acting together at the same time, 'in a group' is the meaning of the idiom.