Given below are two statements.
$Statement-I$ - Skeletal muscles usually derive energy by anaerobic respiration.
$Statement-II$ - After vigorous exercise,lactic acid accumulates in muscle fibres,leading to muscle fatigue.
In the light of the above statements,choose the most appropriate answer from the options given below:

• A
  Both $Statement-I$ and $Statement-II$ are correct.
• B
  Both $Statement-I$ and $Statement-II$ are incorrect.
• C
  Statement $I$ is correct but statement $II$ is incorrect.
• D
  Statement $I$ is incorrect but statement $II$ is correct.