How can a plasmid be described?
a. a small organelle
b. a small loop of dna
c. a prokaryotic ribosome
d. a prokaryotic membrane

Option B,

Explanation:

Plasmids resembles the shape and size of a small circular DNA strand that lies with in the the cytoplasm of a bacterium or protozoan. Thus option B is the correct answer

They are different from normal cell's chromosomal DNA and usually exists naturally in bacterial cells and some Eukaryotas. They  have the ability to replicate independently of the chromosome and thus are mainly used in laboratory for experiments involving gene manipulation

Hence, option B is correct

option c is the correct answer.