C, A, B.
Work Step by Step
As each person leans over, imagine a vertical line passing downward through his CG. If this line extends beyond the area bounded by his feet (i.e., the support base), the person topples over. This is discussed on page 143, and shown in Figure 8.31. Person C has very large feet, a large support base, and the best chance not to topple. Person A and person B have the same size feet, but person A has a skinnier frame and his CM starts out closer to the wall, more within his support base. He has the next-best chance not to topple as he leans over. Person B has the smallest chance of being successful.