Since you titled this "slope of the line", I presume you know how to find that: use the two given points to find the slope of the line. Then find the slope of the line containing one of the given points and one of the possible "answer" points. If the two slopes are not the same, move on to the next answer. If the two slopes are the same, you will need to check other points in that same answer.
However, you are wrong that "a" is the answer- a line through (5, 8) and (3, 8) has slope 0. Perhaps you have copied something wrong- none of those answers is correct.