In an experiment, a researcher gives some patients psychotherapy, gives others medication, and puts others on a waiting list. The researcher then measures how depressed the patients are feeling after six months. What is the independent variable in this experiment?

Which of the following are chemical messengers?

a. Synaptic vesicles b. Receptor sites c. Neurotransmitters d. Potassium ions

There is a steady decline in marital satisfaction in the first few years, followed by a ____

a. plateau and then another decline after nine or 10 years of marriage b. plateau and then a steady increase after the fifth year of marriage c. steady increase for the remainder of the marriage d. steady increase until year 10, then a steady decline