Question

1. the dark, circular is where ribosome assembly begins.
2. the thread - like chromosomes are spread throughout the nucleus in the form of
3. the membrane of the nucleus is dotted with to allow

Explanation:

1. The nucleolus is a dark - circular structure in the nucleus where ribosome assembly starts.
2. Chromosomes exist as chromatin (a thread - like mass) in the non - dividing nucleus.
3. The nuclear membrane has nuclear pores to allow the passage of substances.

Answer:

1. Nucleolus
2. Chromatin
3. Nuclear pores