Which sentence contains an underlined restrictive clause?

The books that are stacked neatly on the top shelf belong to my great-grandfather.
The girl who broke the downstairs window with a baseball is knocking on the front door.
The store allowed the items that were purchased less than thirty days ago to be returned.
The restaurant, which had its grand opening two months ago, is always crowded.

Question

Which sentence contains an underlined restrictive clause?

The books that are stacked neatly on the top shelf belong to my great-grandfather.
The girl who broke the downstairs window with a baseball is knocking on the front door.
The store allowed the items that were purchased less than thirty days ago to be returned.
The restaurant, which had its grand opening two months ago, is always crowded.

Mercury · Answer

thoughts?

as a major hint, recall that restrictive clauses
- are not set apart by commas
- cannot be removed without fundamentally altering the meaning of the sentence