I would say C. at ten o'clock; modifies came. Adverb phrase always involves when, where, or how. In this sentence, you could ask when did the truck came? Then you adverb phrase would it came at ten o'clock.
I hope this helps!
The adverb phrase in the sentence is "at ten o'clock," and it modifies the verb "came." Therefore, the correct option is C. at ten o'clock; modifies came.
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