Answer:
A) Students can make payment for the books when ordering online or when you get them.
(Notice that there is a sentence shift from third person, students, to the second person singular, you.)
B) You can make payment for the books when ordering online or at the point when you get them.
(In this case, both subjects stay in second person.)
C) Students can make payments when ordering online or when they take delivery of the items.
(Students a third person plural noun, requires a third person plural pronoun, they.)
Step-by-step explanation:
In Englich Grammar, a Shift in person refers to the error of improperly mixing first, second, or third person whilst making a spoken or written sentence as shown in A above.
Cheers