If point c is between points a and b, then ac+=ab

the answer would be ac+cb=ab. hope this : -)

d:   bc

step-by-step explanation:

line segment ac and line segment cb add up to ab.   (cb and bc are the same line segment, although one might argue that if they have directions, the directions are opposite one another.)

the battle of gettysburg is considered the "high water mark" of the confederacy because it marked the greatest advance of the confederate forces against the union.