Option A will accept either epsilon or a string that is ending with 1 only,It may happen that string have even no. of 1's but it is ending with 0,So it won't be right answer.
Option B will generate string having only 2 1's,so it won't be the right answer because we are looking for that solution that may generate even strings having even no. of 1's.
Option C will generate string having even no. of 1's so it will be the correct answer.
Option D will generate string having odd no. of 1's so definitely it is not going to be the right answer.
So,according to me C will be the right Regex for generating string having even no. of 1's.
Correct me if I'm wrong.