How are fossils dated?

The example of recapitulation theory is

Homologous organs are those that show similarity in $..........$.

Assertion: Comparative biochemistry provides strong evidence in favour of the common ancestry of living beings.
Reason: The genetic code is universal.

Fossil $X$ is older than fossil $Y$. The most evident answer is:

Choose the correct statements with reference to organic evolution.
$I.$ Flippers of whale and wings of bat exhibit analogy.
$II.$ Wings of butterfly and wings of bird exhibit homology.
$III.$ Organs with dissimilar structure are called analogous organs.
$IV.$ Organs with similar structure and origin are called homologous organs.