Points A, B, C, and D, in that order, lie on a line. If AB = 3 cm, AC = 4 cm, and BD = 9 cm, what is CD, in centimeters?  Choose the most appropriate option.
A) 1 B) 8 C) 3 D) 4 E) 5
Putting a value to each point, lets use the following:   A - 0   B - 3 (AB = 3)   C - 4 (AC = 4)   D - 12 (BD = 9)   CD is 12-4= 
<gadget id="calculator">12-4</gadget>
<output>8</output>
8.   Ans 8
<result>B</result>
Points A, B, C, and D, in that order, lie on a line. If AB = 3 cm, AC = 4 cm, and BD = 9 cm, what is CD, in centimeters?