Final answer:
To separate items in a list that already contain commas, semicolons should be used to ensure clarity and proper understanding.
Step-by-step explanation:
When items in a list contain commas, semicolons are used to separate the items in the list to avoid confusion. Semicolons act as a sort of 'super comma' when the list elements themselves have commas.
For example:
On our trip, we plan to visit Springfield, Illinois; Austin, Texas; and Madison, Wisconsin. In each case, the semicolon is used to indicate the end of one list item and the start of another, making the list clear and easy to read.