中国大学MOOC: _________is a form oftourismor study abroadprogram that allows the visitor to rent a room from a local familyto better learn the local lifestyle as well as improve their language ability.

Which of the following italicized parts serves as an appositive? A: He is not the manto draw back. B: Larry has a large familyto support. C: Tony hit back the urgeto tell a lie. D: There is really nothingto fear.