Which of the following is an example of observational scientific investigation? a noting the color of a solution when heated. b drying solid produced by placing it in an oven. c placing test tubes in an ice bath for 15 minutes. d mixing two reactants together in a small beaker.

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."