(the third one is not supposed to be selected)

Let "a", "b" and "с"  be sides of the triangle ("с" is the longest side). The triangle will be right if  a² + b² = c²

A.
a² + b² = 12² + 13² = 144 + 169 = 313
c² = 25² = 625
313 ≠ 625

B.
a² + b² = 36² + 77² = 1296 + 5929 = 7225
c² = 85² = 7225
7225 = 7225  ←  right triangle

C.
45, 45, 45 ← this is an equilateral triangle (all angles = 60°)

D.
a² + b² = 45² + 56² = 2025 + 3136 = 5161
c² = 67² = 4489
5161 ≠ 4489

Answer is B