In general, the protein quality in grains would be most improved by the addition of a plant protein rich in

The appropriate response is lysine. Lysine is a basic amino corrosive. Many individuals realize that few amino acids are known as the "building squares of protein" and are required all together for a colossal number of appropriate inner capacities, including development. 
There are numerous unbelievable L-lysine benefits, from its utilization as a typical treatment for mouth blisters to a potential against nervousness supplement. As is valid with most supplements accessible in supplement shape, L-lysine can be taken orally yet is assimilated best into the body when devoured through nourishment. It's found in substantial sums in different sorts of meat, beans, cheeses, and eggs.

The right answer is c.sandstone.