A(n) is a repeated behavior that is considered ordinary to the person performing the action.
a. focus
b. habit
c. effort
d. inquiry

A habit is a repeated behavior that is considered ordinary to the person performing the action.

That is because a habit it something that a person has been doing for a long time and cannot leave that habit. 

Depression is lifelong, though you can get medication to with it. the difference between sadness and depression is that sadness lasts a little bit, depression last a long time and it goes on and off. people usually get depression through experiences they have been through, or genetics.