Connor and Mandy Are Two Unrelated 13-Month-Old Infants

Multiple Choice

Connor and Mandy are two unrelated 13-month-old infants. Connor can already walk easily, but Mandy has yet to take her first steps. What is the most likely explanation for the difference between their ability levels?

A) Connor is brighter than Mandy since he is progressing through the stages of development more rapidly.
B) Mandy and Connor are both well within the normal age range for the development of these motor skills.
C) Connor's mother has taught him to walk, but Mandy's mother has not taught her to walk.
D) Mandy's inability to walk at 13 months is abnormal and may indicate the presence of other developmental problems.