Statement $X$ : The cytoskeleton is composed of three types of filaments: microfilaments,microtubules,and intermediate filaments.
Statement $Y$ : Microtubules are hollow tubes made of globular protein tubulin.

• A
  Both Statement $X$ and Statement $Y$ are true. Statement $Y$ is not the correct explanation of Statement $X$.
• B
  Both Statement $X$ and Statement $Y$ are true. Statement $Y$ is the correct explanation of Statement $X$.
• C
  Both Statement $X$ and Statement $Y$ are false.
• D
  Statement $Y$ is false and Statement $X$ is true.