When Must a Partnership Make Mandatory Basis Adjustments

When must a partnership make mandatory basis adjustments?

A) on any sale of a 20% or greater partnership interest
B) on any sale of a partnership interest where the partnership's adjusted basis in its assets exceeds their fair market value by $250,000 or more
C) on any sale of a partnership interest for $250,000 or more
D) on any distribution of assets with a value of $250,000 or more