According to Thomas and Chess's research on infant temperament,which type of temperament is most common

A)  anxious temperament
B)  difficult temperament 
C)  easy temperament
D)  slow-to-warm-up temperament

Temperament

The innate aspect of an individual's personality, including tendencies toward emotional reactivity, intensity, and the general disposition from birth.

Thomas And Chess

Psychologists known for their research in child development and the concept of temperament.

Anxious Temperament

A predisposition to respond with fear, tension, and anxiety to situations that are not inherently threatening.