Which statement about triangles is true?
a. all acute triangles are also equilateral triangles.
b. all right triangles are also isosceles triangles.
c. all equilateral triangles are also acute triangles.
d. some obtuse triangles are also right triangles.

THE ANSWER WOULD BE:

C. ALL EQUILATERALTRIANGLES ARE ALSO ACUTE TRIANGLES.

BECAUSE:

a. cannot be true if the angles are 59, 60, 61.

b. this can also be a right (non-isosceles) triangle 
l \
l  \
l__\

d. if the triangle is obtuse, one angle has to be greater than 90 degrees and if you add a right angle (which is 90 degrees) it would be over the triangle's number of degrees (180)