Given below are two statements regarding evolution.
Statement-$I$: Natural selection is the establishment of a phenotypic trait in changing environmental conditions.
Statement-$II$: Natural selection encourages those genes or traits that ensure highest degree of adaptive efficiency between population and its environment.
In the light of above statements, choose the most appropriate answer from the options given below.

• A
  Both Statement-$I$ and Statement-$II$ are correct.
• B
  Statement-$I$ is incorrect but Statement-$II$ is correct.
• C
  Statement-$I$ is correct but Statement-$II$ is incorrect.
• D
  Both Statement-$I$ and Statement-$II$ are incorrect.