Why light travels slower in glass than in air or vacuum?

because of glass' higher refractive index

Explanation:

air and vacuum have a lower refractive index and are optically lighter, so light travels faster.

whereas glass has a higher optical density, so light travels slower

dopamine..

"it was found that some people who were taking the drug l-dopa to raise their levels of dopamine were developing schizophrenic-like symptoms supporting research a strength of the dopamine hypothesis is that there are many studies which have shown support for the neurochemical explanation."

i think the answer is a, hope this is right, that would be my best guess.