1-59Tracy and Shahid Are Both 3 Months Old

1-59.Tracy and Shahid are both 3 months old.Tracy is highly active,easily irritated,and cries easily.Shahid is quiet,adapts easily to change,and seems fearless.These differences illustrate

A) the impact of shared environmental influences.
B) how physical handicaps can have a genetic origin.
C) differences in temperament.
D) the fact that personality is more influenced by the environment than by genetics.