Which of the following are sentence fragments? i. sarah who works at the cd store. ii. she smiled. iii. at noon tomorrow.

Fragments are sentences that aren't complete due to their lack of at least one independent clause. They may resemble sentences but are not when read clearly.

For the choices above, the first choice, Sarah who works at the CD store. is considered a great example of a fragment sentence and is the correct choice. I am not sure if this is a multiple choice question or a "check all that apply" question. If you are meant to choose only one answer, then go for the first one. However, if you can check more than one, then choose I and III but not II. 

Let me know if you need further info. :)

              - Dotz