Assertion $($A$)$: Mosses along with lichens are the first organisms to colonize rocks.

Reason $($R$)$: They both decompose rocks by scereting acid substances.

$($A$)$ If both the assertion and the reason are trueand the reason is a correct explanation of the assertion.

$($B$)$ If both the assertion and reason are true but the reason is not a correct explanation of the assertion.

$($C$)$ If the assertion is true but the reason is false.

$($D$)$ If both the assertion and reason are false.