The bisector of an obtuse angle forms

a. acute angles
b. right angles
c. obtuse angles
d. straight angles

Option 'a' is correct.

Step-by-step explanation:

Since we know that

Obtuse angles are those angles which is lies between 90° and 180°.

And the bisector of an obtuse angle forms acute angles because of the definition of  an obtuse angle, their bisectors form acute angle.

As we know that the bisectors divides the angle (here, obtuse angle) into two equal and smaller parts.

So, anyhow, it can be acute angles.

Hence, Option 'a' is correct.