i need help!

D: 100.

This happens if 40 is the common angle.

In an islsceles triangle two angles are the same and one is different. 40 could be the different angle or the angle there is two of.

The angles in a triangle sum to 180.

If 40 was the double angle, the third would be 180-40*2=100.

If 40 was the different angle the other two would be (180-40)/2=60.

100 is the largest so D is the answer.