What is the measure of the angle Y made by the diagonals of the any adjacent sides of a cube.  Choose the correct answer.
A) 30
B) 45
C) 60
D) 75
E) 90

Rationale: "c . . 60 degrees all the diagonals are equal . if we take 3 touching sides and connect their diagonals , we form an equilateral triangle . therefore , each angle would be 60 . c"
Answer: C