Nuclear envelope is different from the membranes of other double membrane bound cell organelles in being 

A. The outer membrane studded with ribosomes  

B. Fusion of both outer and inner membrane at certain places.

C. Having contact with endomembrane system. 

D. Having a space between outer and inner membrane.

Nuclear envelope has two membranes named as outer membrane and inner membrane. The outer membrane is continuous with the endoplasmic reticulum and also studded with 80S ribosomes on its outer surface. Both outer and inner membranes are fused at places where nuclear pores are present that regulate the movement of RNA and proteins between the nucleoplasm and cytoplasm. Mitochondria, Chloroplasts and Nucleus have a space between outer and inner membrane and called as perimitochondrial, periplastidial and perinuclear space.