The importance of including a control group

When a gasoline engine burns gasoline, what type of chemical reaction is occurring?

Color blindedness is a sex-linked trait. if we could see the pedigree chart for several more generations of the family illustrated here, we would expect a) more males to be color blind. eliminate b) more females to be color blind. c) no females to ever be color blind. d) an equal number of males and females that are color blind.

In figure 1-2 what is the distance from point b to point c?