The outer membrane of the nuclear envelope is continuous with the membrane of the and is usually covered with attached ribosomes

The endoplasmic reticulum is in continuity with the outer membrane of the nuclear envelope. The ribosomes are attached to these endoplasmic reticulum. Such endoplasmic reticulum with the ribosomes attached to the outer membrane is known as rough endoplasmic reticulum or RER. RER is important in the synthesis as well as processing and transportation of the proteins.

Hence, the blank can be filled with 'endoplasmic reticulum'.

it's     c       this is a cell (b) with a nucleus (c) containing dna (a). the dna is organized into chromosomes (d). a section of the chromosome that codes for a trait is called a gene (e).