I see that OR can be omitted with items in a series:
You can choose from grey, blue, or red.
You can choose to play, study, or sleep.
However, I see cases where or is used multiple times
Ex. 1: You must take EN100 or 125, or EN200, or EN250 before taking this course.
In the case above, should the OR be used multiple times like that? Or can it be used only once like the following?
Ex. 2: You must take EN100, EN125, EN200, or EN250 before taking this course.
Ex. 1 and 2 mean the same thing and gramatically correct?
Thanks in advance.
You must take (EN100, EN125, EN200) or EN250 before taking this course.
You must take one of the four: EN100, EN125, EN200, EN250.
This ambiguity must be avoided, especially in something like instructions on choosing courses where the correct requirements must be met. Hence the repeated or.