The one that is a Pythagorean theorem is the triangle with side lengths 5, 12, 13.
First, let's see if the triangle with side lengths 4, 5, 6 is a Pythagorean triple(The side lengths work for Pythagorean Theorem). We see that 6 is the hypotenuse because it's the greatest side. 42+52 = 41, 41 is not 62 which is 36. So the first option doesn't work
Next, let's see if 15, 6, 10 is a Pythagorean triple, we see again that 15 is our hypotenuse. 62+102= 136, 136 is not= 152 so the second option doesn't
Let's see if 12,8,10 works! 12 = hypotenuse, 82+102=164, 122=144 this means that the third option doesn't work which means the last one is the only option left, though I would memorize these common Pythagorean triples.
The answer is the last option or the triangle with sides 5, 12, 13
Please let me know if you have any questions.