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In which sentence does the first word of the underlined noun clause function as an adverb?

We were waiting to find out who was the starting pitcher.

The announcer let us know that the rain would force a cancellation of the game.

Because of a rain delay, we did not know when the game would start.

Whoever would pitch in the game had a tough battle against the best hitters in the league.

In the sentence "Because of a rain delay, we did not know when the game would start," the first word of the underlined noun clause functions as an adverb.