When a normal distribution is graphed, which of the following are true?
1) There is a continuous, symmetrical distribution in which both tails extend to infinity
2) The mean, median, and mode are identical
3) 68.3 percent of the area lies between the mean and ±2 standard deviations
4) The shape of the curve is determined by the mean and standard deviation

a. 1, 2, 3
b. 2, 3, 4
c. 1, 3, 4
d. 1, 2, 4