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Explanation:
As mentioned earlier (in a previous post) the triangle with sides 2,5,7 is not a right triangle. So we can rule out choice A.
For choice B, we have a = 6, b = 8, c = 10, and that leads to...
a^2+b^2 = c^2
6^2+8^2 = 10^2
36+64 = 100
100 = 100
The true equation at the end means the beginning equation is true as well for those a,b,c values. Therefore, we have a right triangle and the answer is choice B
Choices C and D are similar to choice A. They make a^2+b^2 = c^2 to be false.