Read the paragraph below and answer the questions that follow.
(1) According to researchers, babies can be classified according to their temperament, the general pattern of their emotional reactions to their environments. (2) In the first category are the "easy" babies, who account for about 40 percent of all babies. (3) They are usually in a positive mood, and they adapt well to new situations. (4) Another category contains the "difficult" babies, who make up about 10 percent of all infants. (5) They are often in a bad mood, and they exhibit signs of stress when placed in new situations. (6) The next group, the "slow-to-warm-up" babies, account for 15 percent of all infants. (7) They are moody, and they struggle to adapt to new experiences, but to a lesser degree than the "difficult" babies. (8) In the last group are the "mixed-pattern" babies, the 35 percent of infants who do not fall clearly into any of the other three groups because their moods and reactions are less predictable.
How many categories are there?

A) two
B) three
C) four