A table that shows the age at which infants usually master certain motor skills indicates the averages, or ______, for these skills

A reinforcer that removes something unpleasant from a situation is called a ________ reinforcer

a. positive b. negative c. primary d. secondary

Jeff's parents are thrilled because he has just said his first word -- "Dada." He is most likely about ______ months of age

a. 9 c. 15 b. 12 d. 18