Final answer:
Bok choy is the best source of calcium for someone on a whole-foods plant-based vegan diet, with other good sources being broccoli and whole wheat bread.
Step-by-step explanation:
For someone following a whole-foods plant-based vegan diet, bok choy is an excellent source of calcium. Other plant-based sources of calcium include broccoli, whole wheat bread, and fortified foods. While skim milk is a well-known source of calcium, it is not vegan, as it is an animal product. Vegans can also obtain calcium from green leafy vegetables, nuts, beans, seeds, and certain fortified plant milks and juices.