Sample exam question-explanation please?

[Panopticon]

Otters have special oil glands that help make their fur water repellant [sic]. The cells that make up the oil
gland are likely to have abundant

a. rough endoplasmic reticulum
b. smooth endoplasmic reticulum
c. spliceosomes
d. nucleoid regions
e. signal recognition particles

The correct answer is smooth ER, but why is this the case?

[JackBean]

look where are lipids synthesised