Which of the following statement is true for a parallelogram?

1. Its diagonals are equal.

2. Its diagonals are perpendicular to each other.

3. The diagonals divide the parallelogram into four congruent triangles.

4. The diagonals bisect each other.

Which of the following is not true for a parallelogram?

1. opposite sides are equal

2. opposite angles are equal

3. opposite angles are bisected by the diagonals

4. diagonals bisect each other

If the diagonals of a square ABCD intersect each other at O, then △OAB is

1. an equilateral triangle

2. a right angled but not an isosceles triangle

3. an isosceles but not right angles triangle

4. an isosceles right angled triangle.

If the diagonals of a quadrilateral PQRS bisect each other, then the quadrilateral PQRS must be a

1. parallelogram

2. rhombus

3. rectangle

4. square