Final answer:
The Maasai people in Tanzania and the Fula people in Nigeria, who both have lactase-persistence, are likely more closely related to each other compared to the Chagga people in Tanzania.
Step-by-step explanation:
The Maasai people in Tanzania and the Fula people in Nigeria are both lactase-persistent, meaning they can digest lactose in milk. On the other hand, the Chagga people in Tanzania are not lactase-persistent. To determine which groups are most closely related, we can look at the presence or absence of lactase-persistence. Since the Maasai and Fula people both have lactase-persistence, they are likely more closely related to each other compared to the Chagga people. Therefore, the answer is 4) Maasai and Fula.