For any triangle, the third side must be greater than difference of two sides and less than the sum.
Let the third side be x.
for 2, 4 x > 2, x < 6.
8 does not fit in, so 2,4, 8 can't form triangle
for 3, 5 x > 2, x < 8.
7 does fit in, so 3,5, 7 can form a triangle.
Testing the others in the same, doesn't form the sides of a triangle.
So only set B 3,5,7 could be the side lengths of a triangle.
