If $f\left(x\right)=x^2+\lambda x+\mu$ be an integral function of the integral variable x then

• A

  $\lambda$ is an integer and $\mu$ is a rational fraction 

• B

  $\lambda$and $\mu$are integers

• C

  $\mu$ is an integer and $\lambda$ is a rational fraction

• D

  $\lambda$ and $\mu$ are rational fractions