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
I have no idea what the answer is, pls help me

Answer 1

for right triangles ... a^2 + b^2 = c^2 ... Pythagorean Theorem
... so the three sides can't be equal

Answer 2

D- all equilateral triangles have angle measurements of 60 degrees, and right triangles have one 90 degree angle, making a right equilateral triangle impossible to construct

Answer 3

Its D because they have the measurement of 60 degrees and right triangles have a 90 degree angle.