According to the endosymbiotic theory, why was it adaptive for the larger (host) cell to keep the engulfed cell alive, rather than digesting it as food select all that apply

It provides ATP.

Explanation:

It is adaptive for the larger host cell to keep the engulfed cell alive, instead of digesting it as food because the engulfed cell provides energy in the form of adenosine triphosphate (ATP) to the host cell. The larger host cell is able to survive in anaerobic conditions with the help of engulfed cell alive so that's why we can conclude that the larger host cell keep the engulfed cell alive instead of killing it and used as a food source.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands