Select the most appropriate meaning of the given idiom. Mull over

An idiom is a fixed phrasal expression whose overall meaning cannot be worked out from the literal sense of its individual words. The phrasal verb 'to mull (something) over' means to think about something carefully and for a considerable time before reaching a decision or conclusion — to deliberate or ponder over it.

Applying this to the given idiom, 'mull over' expresses the act of turning a matter over in one's mind and weighing it thoughtfully — precisely the sense carried by the word 'Ponder'.

Contrasting this with the other choices:

• 'Guise' refers to an outward appearance or a false pretence adopted to conceal one's real nature or intent — a sense unrelated to thinking something through.

• 'Lament' means to express grief, sorrow, or regret over something — it conveys emotion, not a process of careful thought.

• 'Latter' is a positional reference term denoting the second of two things already mentioned — it carries no meaning related to reflection or consideration.

Therefore, the idiom 'mull over' most appropriately means 'Ponder'.