An analytical essay;

a. is a personal story or description.

b. often incorporates outside source material.

c. usually pulls from material the writer already knows.

d. is a type of creative writing that allows an informal style

An analytical essay often incorporates outside source material. The answer is option B. Analytical essays need to incorporate outside source materials in order to support the writer's analysis and interpretation to a certain thing such as a book, poem, event, or even a work of art because it needs to have reliable basis as to why the writer came up which such analysis.