Sentences often contain lists of items. When a list within a sentence contains three or more items, use a serial comma before the final item.
However, if any item in a list of three or more items already contains commas, use semicolons instead of commas between the items.
To draw more attention to the items and help readers understand the separate, parallel items in a complex list, use lowercase letters in parentheses before each item. Do not use numbers in parentheses.
Participants provided information about their (a) level of education; (b) income, specified at the family level; (c) occupation, including both specific role and industry; and (d) family size.