<span>Option B. Arrange four-length sides so the diagonals are equal in length. Since a square is a rectangle with four equal sides the diagonals should bisect each other at each length and at 90 degrees to each other. This is really important. If the diagonals are equal in length and bisect each other at equal distance then the sandbox is measuring length and has equal angles which is a square by definition</span>
P(A and B) = 0 when events A and B are disjoint, aka mutually exclusive.
We say that two events are mutually exclusive if they cannot happen at the same time. An example would be flipping a coin to have it land on heads and tails at the same time.