Given below are two statements:
Statement $I$: Bohr's theory accounts for the stability and line spectrum of $Li^{+}$ ion.
Statement $II$: Bohr's theory was unable to explain the splitting of spectral lines in the presence of a magnetic field.
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 true.
• B
  Statement $I$ is false but statement $II$ is true.
• C
  Both statement $I$ and statement $II$ are false.
• D
  Statement $I$ is true but statement $II$ is false.