In the given figure,which substance is synthesized by the part labeled $A$?

$S$ - Statement: $RNA$ and protein molecules move between the nucleoplasm and the cytoplasm.
$R$ - Reason: Nuclear pores are present at several locations in the nuclear envelope of the nucleus.

$L-$ shaped chromosomes are called

The given diagram shows the types of chromosomes (labelled as $A, B, C$ and $D$) based on the position of the centromere. Which one is the correct option for the labelled chromosomes $A, B, C$ and $D$?

$DNA$ is found primarily in:

Describe the composition, structure, and types of chromosomes.