Choice C is the best answer. This question tests punctuation with conjunctive adverbs.

1. Context clues: Two independent clauses connected by "nonetheless."
2. Meaning: Use semicolon before and comma after conjunctive adverbs.
3. Verify: "The initial costs were higher than anticipated; nonetheless, the board approved..." is correct.

💡 Strategy: Use semicolon + conjunctive adverb + comma between independent clauses.

Choice A is incorrect because a comma before "nonetheless" creates a comma splice. Choice B is incorrect because it lacks the semicolon. Choice D is incorrect because a colon doesn't precede conjunctive adverbs.