Answer: Massachusetts.
Explanation: The surface of El Salvador is around 21,041 km^2, we need to see which of the given option has almost the same surface.
The surface of Wisconsin is 169,639 km^2
The surface of California is 423,970 km^2
The surface of Rhode Island is 3,140 km^2
The surface of Massachusetts is 27,363 km^2
The closest one to El Salvador is the state of Massachusetts.