Which organelle possesses flat,disc-shaped sacs or cisternae and is found near the nucleus?

Endoplasmic reticulum is more developed in:

Identify the components labelled as $A$,$B$,$C$,and $D$ in the diagram given below from the list $(i)$ to $(viii)$.
$(i)$ Cristae of mitochondria $(ii)$ Inner membrane of mitochondria $(iii)$ Cytoplasm $(iv)$ Smooth endoplasmic reticulum $(v)$ Rough endoplasmic reticulum $(vi)$ Mitochondrial matrix $(vii)$ Ribosome $(viii)$ Nucleus

In the Golgi apparatus,each stack contains .......... cisternae.

In animal cells,the synthesis of lipids like steroid hormones occurs in the .......... endoplasmic reticulum.

Which cell organelle divides the intracellular space into two distinct compartments,i.e.,$luminal$ (inside the endoplasmic reticulum) and $extra-luminal$ (cytoplasm)?