Answer is option c;
This follows from pigeon hole principle
In worst case,you take only 1 shoe from every pair.
Now if you take a shoe from the remaining 10 shoes
you will definitely have a pair.
Ps:
Thing is we try to avoid getting pair of shoes as much as we can.when we pick 10 shoes (1 from each pair),we can't avoid getting a pair further.Hence any shoe taken now will form a pair