According to the text, about what percentage of cohabiting couples in the U. S. today are over the age of 40:

Sheila is a biology major and hopes to go to med school, but she enjoys spending a couple of hours every weekend practicing the flute. Her flute playing reflects

A) intrinsic motivation. B) an effort attribution. C) social capital. D) communities of practice.

In the flip-flop circuit that controls sleep and arousal, the ___________ neurons are the stabilizing force, pushing the circuit toward arousal

a. orexinergic b. serotonergic c. noradrenergic d. cholinergic e. dopaminergic