Which sentence below is properly punctuated?

a. babette followed her boss's example: when he left for the day, she disappeared.
b. babette followed her boss's example, when he left for the day, she disappeared.
c. babette followed her boss's example when he left for the day, she disappeared.

A

Explanation:

A semicolon is necessary to distinguish the "introductory" phrase from the introduced element, and that role cannot be fulfilled by a comma as in the second option, much less by the absence of punctuation as in the third option, which makes the sentence even more chaotic.

the: determiner

storm: noun

remains: verb

a: determiner

threat: noun

to: preposition

the: determiner

coastal: adjective

village: noun