Question

the hubble tuning fork diagram for galaxies is useful because it
organizes galaxies according to their size and metallicity.
categorizes galaxies by shape and appearance.
provides an objective way to classify galaxies that does not vary between observers.
shows how galaxies change over time.

Explanation:

The Hubble tuning - fork diagram is a visual classification of galaxies based on their morphological (shape and appearance) characteristics such as ellipticals, spirals, and barred - spirals. It does not consider size and metallicity in its basic classification, nor is it completely objective as different observers may have some variation in interpretation, and it does not directly show how galaxies change over time.

Answer:

categorizes galaxies by shape and appearance.