Pourquoi doit on toujours préciser le référentiel dans le quel est étudié le mouvement d'un système?

The movement of an object depends on the reference frame, so it is important to predicate it.

Explanation:

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."

the answer is b, have negligible mass