Adouble-blind study of a vaccine is one in which : the study group receives the vaccine and the control group receives a placebo. neither observer nor subjects know the nature of the placebo. neither observer nor subjects know which subject receives the vaccine and which receives a placebo. neither the study group nor the control group knows the identity of the observers. the control group does not know the identity of the study group.

Neither observer nor subjects know which subject receives the vaccine and which receives a placebo

Explanation:

In a double-blind study neither the participants nor the experimenters is aware of who is receiving a particular treatment.

Its used to prevent bias in research results from demand characteristics or the placebo effect

mammal

explanation:

endo:

regulates body hormones, aldosterone, vasopressin

neural:

signal, regulates body using electric signals, reflex

endo has to do with hormones; aldosterone and vasopressin are both hormones. i also had this question and got it right : d