Which of the following are tautologies (statements that are always true)? Assume x and y are boolean variables.

1. Correct Answer
   Incorrect Answer
   a

   (x && y) || (!x && !y)

2. Correct Answer
   Incorrect Answer
   b

   !(x || !x)

3. Correct Answer
   Incorrect Answer
   c

   x || !x

4. Correct Answer
   Incorrect Answer
   d

   x || y

5. Correct Answer
   Incorrect Answer
   e

   y && (!y || y)