Which of the following is true about imprinting?
a. it is often used in the training of adult animals.
b. it is restricted to birds.
c. it always involves the sense of sight.
d. it occurs during a specific time in young animals.

The correct answer is the following one:
d. It occurs during a specific time in young animals.

It is not restricted to birds, as some mammals also imprint. It can involve the sense of sight, but it can also involve other senses, such as the sense of smell and the sense of hearing.