Which two punctuation marks are used to offset a parenthetical element in a sentence?

I'm gonna say that the answer is a Comma and semicolon.

Three punctuation marks are commonly used to show a parenthetical phrase: commas, parentheses, and dashes. The following table shows when each punctuation mark is best used.

Since there is only two in the list of answers that match this fact, it has to be comma and dash.