Explanation
Correct answer: C.
Choice C is the best answer. The convention being tested is the punctuation of an integrated relative clause. No punctuation is needed before the relative clause beginning with "that" because the content of the relative clause ("that...Lighthouse") is integral to the meaning of the coordinated adjectival phrase ("so bright, so localized, and so dependable") that it modifies.
Why the other choices are wrong
Choice A
Choice A is incorrect because no punctuation is needed between the coordinated adjectival phrase ("so bright...dependable") and the integrated relative clause that modifies it.
Choice B
Choice B is incorrect because no punctuation is needed between the coordinated adjectival phrase ("so bright...dependable") and the integrated relative clause that modifies it.
Choice D
Choice D is incorrect because no punctuation is needed between the coordinated adjectival phrase ("so bright...dependable") and the integrated relative clause that modifies it.