Which triangle is not possible to construct?

Question

A a right isosceles triangle
B an acute equilateral triangle
C an obtuse scalene triangle
D a right equilateral triangle

This is the second time ive posted but the last thread got confusing

Answer 1

Please study these definitions and pictures of different kinds of triangles.

http://www.mathsisfun.com/definitions/isosceles-triangle.html

Which of your choices is impossible?

Answer 2

I already went through trying to draw a 60, 60, 60, 90 triangle with this student.