参考答案：

#include<iostream>
#include<algorithm>
using namespace std;
string s[10];
bool cmp(string a, string b)
{
    return a.size() < b.size();
}
int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        for (int i = 0; i < 4; ++i) cin >> s[i];
        sort(s, s + 4, cmp);
        if (s[0].size() < s[1].size())
        {
            cout << s[0][0] << endl;
        }
        else if (s[3].size() > s[2].size())
        {
            cout << s[3][0] << endl;
        }
        else cout << 'C' << endl;
    }
    return 0;
}