If you are looking for the difference of squares, the two terms both have to be squares. We know that 64 is a square because it is 8 x 8. Also, we can say 4x^2 is a square because it can also be written as (2x)^2. We are basically looking for an option that tells us that they are square. This is option 1.
The second option is invalid because being an even number does not mean the number is a square.
The third option does not help the case much either. Just because there is a common perfect square factor, does not mean the numbers themselves are perfects squares.
