Final answer:
The sentence 'He's going to end his addiction for good.' contains the idiom 'for good', which means permanently and is not intended to be understood literally. Therefore, the correct answer is a) ""He's going to end his addiction for good."
Step-by-step explanation:
The sentence that contains an idiom that starts with a preposition is 'He's going to end his addiction for good.'
Here, 'for good' is the idiom which means 'permanently' or 'forever.' This phrase acts as an adverb describing the verb 'end.' An idiom is not meant to be taken literally; it's a figurative expression that has become a fixed part of the language and conveys a specific meaning known to native speakers.
Examples of other idioms starting with prepositions include phrases like 'on the ball,' meaning to be alert and efficient, or 'at stake,' meaning in a risky situation or subject to loss.