#include <stdio.h>

#define NUMBER_OF_ALPHABET 26
#define MAX_STRING_LENGTH 255

int main(void)
{
	int i, j, k;
	int cursor;
	int maxCount, maxCountIndex;
	int numberOfTestcase;
	int countAlphabet[NUMBER_OF_ALPHABET];
	char inputString[MAX_STRING_LENGTH];
	bool flag = false;

	scanf("%d\n", &numberOfTestcase);

	for(i = 0; i < numberOfTestcase; i++)
	{
		for(j = 0; j < NUMBER_OF_ALPHABET; j++)
		{
			countAlphabet[j] = 0;
		}
		scanf("%[ a-z]", &inputString);

		cursor = 0;
		while(inputString[cursor] != '\0')
		{
			if(inputString[cursor] != ' ')
			{
				countAlphabet[inputString[cursor]-'a']++;
			}
			cursor++;
		}
		maxCount = 0;
		maxCountIndex = 0;
		for(k = 0; k < NUMBER_OF_ALPHABET; k++)
		{
			if(countAlphabet[k] > maxCount)
			{
				maxCount = countAlphabet[k];
				maxCountIndex = k;
				flag = false;
			}
			else if(countAlphabet[k] == maxCount)
			{
				flag = true;
			}
		}
		if(flag)
		{
			printf("?\n");
		}
		else
		{
			printf("%c\n", maxCountIndex+'a');
		}
		fflush(stdin);
	}	

	return 0;
}