I feel that only choices C and E seem relevant, and I will choose E.
To solve this CR, we are required to choose the answer choice that best supports the claim that "in spite of this increase, advertisers will continue to profit from television advertising"
Choice A neither supports not weakens the argument made by the TV executives.
Choice B is irrelevant.
Choice D is out, because it does not address the executive's claim.
Choice C - If TV spots less than 30 seconds are not available, then advertiser's will be spending more on ads, and I am not sure, whether the TV executives are referring to this increase in spending. As I am probably making an unstated assumption, lets skip this choice.
Choice E is the safest. If the number of people watching TV is increasing, then it will mean that, advertisers are reaching a larger audience. Thus when compared to last year, an advertiser will be paying a little less per member of the audience next year (despite the increase), when compared to the amount per audience member last year. I did a bit of math, to support my argument.
If there were 100 members watching TV programs last fall, then the rate of increase will result in 126 members watching TV programs, by the start of next fall, when the advertisers are only paying 110 to 115% of what they spent last year.
Thus E.