The increase in the number of American households viewing telecasts of NASCAR races
imply that the motorsport will soon supplant NFL football as the nation's most popular sport, but that the limited number of races each year compared to the NFL's hundreds of games indicates that fans will continue to watch football at a significantly higher rate.
A) imply that the motorsport will soon supplant NFL football as the nation's most popular sport, but that
B) imply that the motorsport is soon supplanting NFL football as the nation's most popular sport, but
C) implies that the motorsport will soon supplant NFL football as the nation's most popular sport, but that
D) implies that the motorsport is soon supplanting NFL football as the nation's most popular sport, but that
E) implies that the motorsport will soon supplant NFL football as the nation's most popular sport, but
Notwithstanding the unsound and ugly 'motor sport is soon supplanting' in D:
The reason why D is wrong is more that the 'but that' structure gives an absurd twist to the meaning. We normally mean to say that if there are two factors namely X and Y caused by some A factor, then we have to use the 'but that ' structure for both the factors X and Y to maintain parallelism. However, if the Y factor is not relevant or is extraneous to the A factor, then using the 'but that' structure will give an absurd meaning. To wit:
The increase in the number implies that the motorsport is soon supplanting -- Ok this is acceptable because the survey is about NASCAR races and the result is also about the motor race. However, the second factor namely that the NFL viewership will outperform the races viewership is not suggested by the survey; the second part is an extraneous and independent comment and therefore D is wrong.
You might see where but that is going to be relevant to //ism.
A report by GMAC indicates that Asians outperform both Americans and Europeans in Quants, but that the Asians underperform in Verbals.
Here one cannot do away with the 'but that' structure. If you drop the 'but that' phrase in the second factor, then the sentence will be un//.