Abdc is a trapezoid. line ab = 2.5, and line ef = 4.5. what is the length of line cd ? 7.0 2.0 3.5 3.75

The line CD is the median of thre trapezoid, therefore its measures is shown below:
 You must sum the largest base and the shortest base and divide both of them by 2, as following:
 CD=(4.5+2.5)/2
 CD=7/2
 CD=3.5
 Therefore, as you can see, the measure of the line CD is 3.5
 The answer is: 3.5