Fossil $X$ is considered to have evolved before fossil $Y$. This is true if:

• A
  $Y$ are vestigial structures that are homologous to the structures of $X$.
• B
  $Y$ is structurally more complex than $X$.
• C
  $Y$ is in a better state of preservation than $X$.
• D
  $X$ is found in lower sedimentary strata than $Y$.