19. 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,

Answer is A. I picked something else because I thought "continue" should've been "continueS" because "the present rate" is singular. Can someone explain why it is plural? It doesn't conform to the subjunctive mood rule: "bossy verb or If" + that. This is backward. This it still count?



22. Kuru, one of the strangest and most insidious of the diseases known, is no longer a major problem in New Guinea.
(A) of the diseases known
(B) of the diseases to be known
(C) of the diseases that is known
(D) known of the diseases
(E) diseases known



I picked E. Wrong. I don't know why B is right. Can some one explain? Thanks.