In Their Studies of Infant Monkeys, How Could Harlow and His

In their studies of infant monkeys, how could Harlow and his colleagues tell when monkeys were attached to their surrogate mothers?

A) The monkeys would prefer to look at the surrogate mother that had fed them.
B) The monkeys would only take milk from the mother to which they were attached.
C) The monkeys would run to the surrogate mother when frightened by a strange object, then use the mother as a base from which to explore.
D) Their later social interactions with other monkeys were normal if they had been raised by a surrogate to which they had become attached.