Statement $A$: The name 'Reptilia' is derived from the Latin word 'repere' or 'reptum',which means 'to creep' or 'to crawl'.
Statement $B$: Since they creep or crawl,it is not necessary that all animals of the class Reptilia are limbless.

• A
  $A$ and $B$ are both true and $B$ is the correct explanation of $A$.
• B
  $A$ and $B$ are both true,but $B$ is not the correct explanation of $A$.
• C
  $A$ is true and $B$ is false.
• D
  $A$ is false and $B$ is true.