Answer:
(C) is correct option.
Explanation:
The loudness of sound wave determines its amplitude. If the sound is loud, it will have more amplitude while if the sound is soft, it will have less amplitude.
On doubling the amplitude of sound wave, it will become more loud.
Doubling the amplitude of a sound wave will leave the speed of sound unchanged, but cause the sound to be louder. Hence, the correct option is (C).