Which of the following is not one of the nine symptoms of depression:

a. dysphoric mood, anhedonia, significant weight loss/gain,
b. insomnia or hypersomnia, feelings of worthlesness or inappropriate guilt,
c. diminished ability to think/concentrate, unusual motor behavior (i. e. catatonia),
d. recurrent thoughts of death or suicidal ideation

c. diminished ability to think/concentrate, unusual motor behavior (i.e. catatonia)

Explanation:

This is not a symptom of depression among the nine prominent symptoms since thinking process or concentration is normal or high in depression since the human mind is too preoccupied. A person suffering from depression does not commit unusual motor behavior such as catatonia since this is the symptom normally found in persons suffering from schizophrenia.

i really need the answer guys

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.