The correct answer is A. straight leg hamstring stretch and calf stretch
In a marathon (long run) the muscles you use the most are your leg muscles, which include your calves, quadriceps and hamstrings. Therefore, it is best to stretch and warm up these muscles prior to a marathon run. Option B, C and D, would not be as useful for a marathon run since they involve stretching your arms, shoulders, neck and saddle muscles rather than your leg muscles. I have attached photos of what a straight leg hamstring stretch and calf stretch look like for your reference.