The sentence is divided into four segments: (A), (B), (C), and (D). Identify the segment that contains a grammatical error. If the sentence is both grammatically and contextually correct, select "No error" as the correct answer.

The speaker had scarcely (A)/ begun the address (B)/ than the power went (C)/ out completely. (D)

The correct answer is C.

Explanation:
The given sentence is divided into four segments:
"The speaker had scarcely (A)/ begun the address (B)/ than the power went (C)/ out completely. (D)"

In English grammar, the correlative conjunction scarcely (or hardly) is paired with when (or before), not than.
(Note: No sooner is paired with than).

In segment (C), the conjunction than is incorrectly used. To correct the sentence, "than" should be replaced by "when".

Corrected Sentence:
"The speaker had scarcely begun the address when the power went out completely."

Therefore, segment (C) contains the grammatical error.