Question

which characteristic is used to classify galaxies? the size of the galaxy the shape of the galaxy the presence of dust and gas between stars the presence of active star formation sites

Explanation:

Galaxies are primarily classified based on their shapes. The most common classification schemes like the Hubble sequence categorize galaxies as elliptical, spiral, and irregular depending on their form. Size, presence of dust - gas between stars, and active star - formation sites are important characteristics but not the main ones for classification.

Answer:

the shape of the galaxy