Option A: 
Option D: 
Step-by-step explanation:
Option A: 
To find the sides of a square, let us use the distance formula,

Now, we shall find the length of the square,

Thus, the square with vertices  has sides of length a.
 has sides of length a.
Option B: 
Now, we shall find the length of the square,

This is not a square because the lengths are not equal.
Option C: 
Now, we shall find the length of the square,

Thus, the square with vertices  has sides of length 2a.
 has sides of length 2a.
Option D: 
Now, we shall find the length of the square,

Thus, the square with vertices  has sides of length a.
 has sides of length a.
Thus, the correct answers are option a and option d.