As a part of their longitudinal study Thomas and Chess (1956) revisited subjects years after the original classifications of temperament. Years later, Subject "A" is described as being "sometimes fearful, having problems academically, and at times, he lingers in his response to social cues." Which of the following temperament categories does Subject "A" fit?

a. easy
b. difficult
c. slow-to-warm-up
d. undifferentiated

C. Slow-to-warm-up babies rarely seemed to have problems in early childhood, but once they entered school they were sometimes fearful and had problems academically and with peers because of their relatively slow responsiveness.