Which of the following is a method of preservation?

Why is the importance of botanical gardens increasing?

The importance of botanical gardens is increasing due to the conservation of these plants.

$S$ Statement: Zoological parks serve as centers for learning about the conservation of wildlife.
$R$ Reason: Botanical gardens are used to establish seed banks where gene pools are created for the preservation of rare genes.
$(a)$ Both $S$ and $R$ are true,and $R$ is the correct explanation of $S$.
$(b)$ Both $S$ and $R$ are true,but $R$ is not the correct explanation of $S$.
$(c)$ $S$ is true and $R$ is false.
$(d)$ $S$ is false and $R$ is true.

What is the importance of a Herbarium?

Why are botanical gardens necessary?