The double membrane around the nucleus is called the

C. nuclear envelope

Explanation:

The nucleus is surrounded by a double membrane, known as the nuclear envelope, with nuclear pores. Mitochondria - this is the site of aerobic respiration within the cell. They are surrounded by a double membrane (envelope), with the inner membrane folded into finger-like projections called cristae.

the tricuspid valve is present between right atrium and right ventricle