Behavior modification techniques work best with problems that manifest itself in overt actions.

Itself

Answer: C Test point: the number of consistent pronouns. Analysis: pronouns person and number with the noun it refers to generation. Here refers to the plural noun problems, plural pronouns should use themselves. Problem solving points: singular and plural forms of pronouns is TOEFL often test points, we must find the noun it is meant to be used to determine their number are the same.