In one study described in the textbook, infants with difficult temperaments were randomly assigned to either a condition in which their mothers received sensitivity training or a condition in which their mothers received no training. In this study, infants whose mothers received sensitivity training were in the group.

The answer is an experimental group.

Explanation:

An experimental group, also called a treatment group, consists of a group that usually receives some kind of treatment during an experiment. The group is usually composed of test subjects like people, animals, plants, among others. The treatment refers to the variable that is being studied.

When the group does not get the appropriate treatment is called the control group. There is one difference between the control group and the experimental group and it could be the hypothesis you are working with.      

what is the answer

answer; /// you data to develop general ideas or theories;