The suffix -poiesis means:

A) spitting.
B) prolapse.
C) before.
D) formation.

-poiesis

A suffix meaning the formation, production, or generation of something, such as in 'hemopoiesis' the production of blood cells.

Suffix

A morpheme added at the end of a word to form a derivative, e.g., -tion, -sion, -ness.

Formation

The process of developing or being formed; in biology, it often refers to the way cells or tissues are created and organized.