Answer
d.
Work Step by Step
a. is true since, when in cyclic mode, the electron from photosystem I is passed to the cytochrome b6-f complex for ATP production, from which it can return to photosystem I, but under noncyclic conditions, an electron from photosystem II eventually ends up in photosystem I. b. is incorrect since this is true ultimately but the splitting of water is distant from the events discussed in this question. a. is awkwardly worded, so someone might say that it is not true if they were reading the answer to mean that the electron goes right back to the photosystem with ATP generated there rather than by the cytochrome b6-f complex.
