According to some experts, carbon dioxide is accumulating in the atmosphere so rapidly, largely because of the burning of fossil fuels, that should the present rate of buildup continue, the global concentration of this poison will double by the end of the next century.
(A) that should the present rate of buildup continue, the global concentration of this poison
(B) should the present rate of buildup continue, the global concentration of this poison
(C) should the present rate of buildup be continued, the global concentration of this poison
(D) the global concentration of this poison, were the present rate of buildup continue,
(E) that the global concentration of this poison, if the present rate of buildup did continue,