Gajjo and Bottle

Gajjo has a bottle on which he wants to paste a sticker of string. Initially Gajjo has two strings and the resultant string should be the concatenation of both the string but Gajjo doesn't want characters common between the strings to be present in the resultant string. Help Gajjo find the string that he will paste on his bottle. ###Input: - First line will contain $T$, number of test cases.