Final answer:
The major food source for the Ju/Wasi during the time of Richard Lee's study was mongongo nuts, which constituted nearly half of their diet at certain times of the year and provided essential nutrients.
Step-by-step explanation:
The major food source for the Ju/Wasi during the time of Richard Lee's study was c) mongongo nuts. Despite the availability of various foods such as grains, meat, and fish in different regions, the Ju/'hoansi people, living in the harsh environment of the Kalahari Desert, depended heavily on mongongo nuts. These nuts are not only highly nutritious and drought-resistant, but they also provide a substantial amount of calories and protein. At certain times of the year, mongongo nuts made up nearly half of the Ju/'hoansi diet, highlighting their essential role as a staple food.