A normal curve: Select one: O a. Does not often occur in nature. O b. Is bimodal . O c. Is skewed . O d. Is also called a bell-shaped curve. When a curve has a tail to the right but no tail to the left, it is said to have a: Select one: O a. Positive skew. O b. Negative skew. O c. Bimodal distribution. O d. Normal curve. Measures of central tendency include: Select one: O a. The mean, average and percentage. O b. The mean, median and middle. c. The mean, median and mode. O d. The mean, mode and maxim