Question

British scientist John Allen states that cells containing chloroplasts and mitochondria are complex, creating unique genes and proteins. Allen believes that cells containing chloroplasts and mitochondria came to exist because organelles such as

a
mitochondria engaged in reactions that benefited simple cells and recent complex cells on a single occasion.
b
chloroplasts engaged in reactions that benefited recent complex cells.
c
mitochondria engaged in reactions that benefited early simple cells.
d
chloroplasts engaged in reactions that temporarily benefited early simple cells and recent complex cells.