The Dominator of Strings

Here you have a set of strings. A dominator is a string of the set dominating all strings else. The string $S$ is dominated by $T$ if $S$ is a substring of $T$.

The input contains several test cases and the first line provides the total number of cases.
For each test case, the first line contains an integer $N$ indicating the size of the set.
Each of the following $N$ lines describes a string of the set in lowercase.
The total length of strings in each case has the limit of $100000$.
The limit is 30MB for the input file.

For each test case, output a dominator if exist, or No if not.

3
10
you
better
worse
richer
poorer
sickness
health
death
faithfulness
youbemyweddedwifebetterworsericherpoorersicknesshealthtilldeathdouspartandpledgeyoumyfaithfulness
5
abc
cde
abcde
abcde
bcde
3
aaaaa
aaaab
aaaac

youbemyweddedwifebetterworsericherpoorersicknesshealthtilldeathdouspartandpledgeyoumyfaithfulness
abcde
No

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