The correct answer is 'hat at store 1'. The given code defines a string 'hat at store' and finds the index of the substring 'at', which occurs at index 1. The substring operation is performed but not assigned to any variable, so it does not modify the original string. When 's.indexOf("at")' is called the second time, it again returns 1. As a result, the printed output is the original string followed by the found index of the substring 'at', resulting in 'hat at store 1'.