Which of the following components are included in the structure of the nucleus?

Match the parts of the chromosome given in Column $I$ with their explanation in Column $II$:

Column $I$ (Chromosome)	Column $II$ (Explanation)
$1$. Centromere	$a$. Disc-shaped plate where spindle fibres get attached during cell division.
$2$. Secondary constriction	$b$. Long unbranched slender highly coiled $DNA$.
$3$. Kinetochore	$c$. Place where $2$ chromatids are joined together.
$4$. Chromatonema	$d$. Nucleolus gets organised at this place.

Choose the correct answer from the following options.

Balbiani rings are sites of

Polytene chromosomes have a common point of attachment. What is this point called?

The function of the nucleolus is the synthesis of

The main axis of lampbrush chromosome is made up of..........