In the Early 20th Century,some Astronomers Incorrectly Believed That They

In the early 20th century,some astronomers incorrectly believed that they could observe features in spiral nebulae rotate over the course of a few years.If those observations were correct,what would they have immediately suggested about the nature of these nebulae?

A) that they were island universes
B) that they were inside the Milky Way
C) that they were forming stars
D) that they were accretion disks