The decay constant of a radioactive sample is $\lambda$. The half-life and mean life of the sample are respectively

• A
  $\frac{1}{\lambda}, \frac{\ln 2}{\lambda}$
• B
  $\frac{\ln 2}{\lambda}, \frac{1}{\lambda}$
• C
  $\lambda \ln 2, \frac{1}{\lambda}$
• D
  $\frac{\lambda}{\ln 2}, \frac{1}{\lambda}$