Statement $I$: An alloy of lithium and magnesium is used to make aircraft plates.
Statement $II$: The magnesium ions are important for cell-membrane integrity.
In the light of the above statements,choose the correct answer from the options given below.

• A
  Both Statement $I$ and Statement $II$ are true.
• B
  Both Statement $I$ and Statement $II$ are false.
• C
  Statement $I$ is true but Statement $II$ is false.
• D
  Statement $I$ is false but Statement $II$ is true.