Which of the following foodstuffs was cultivated in the missions?

The correct choice highlights that cereal grains were indeed cultivated in the missions. During the Spanish colonial period in California, missions were established not only as religious outposts but also as agricultural hubs. The cultivation of various cereal grains, such as wheat, barley, and maize, was essential for supporting the mission populations and the local communities.

Cereal grains provided a staple food source, which was crucial for sustaining the mission's residents and the wider population. The success of grain cultivation was also indicative of the missions' adaptability to their environment and their role in the economic development of the region.

While exotic tropical fruits, wheat exclusively, and only vegetables might seem feasible, they do not fully encapsulate the broader agricultural practices within the missions. The missions grew a diverse array of crops, including different types of grains, which is why acknowledging the cultivation of cereal grains is more accurate and encompassing.