Which set of three numbers could be better he side lengths of a triangle

The sides of a real triangle satisfy the triangle inequality, which just says any two sides add up to more than the third.  It's strictly more; if two sides add up to exactly the third that's called a degenerate triangle.  It's not a real triangle because the vertices are three collinear points.

The triangle equality fails when the sum of the two smallest sides fails to exceed the the largest side.

A.  4+6=10, degenerate triangle, not a real triangle

B.  4+7>7, isosceles triangles are real, SELECT

C. 4+3<10, not a real triangle

D. 4+7=11, degenerate triangle again

20000 as first it increases by 2500 then by 5000 so next it will increase by 10000