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Hi jasmeet, though I wouldn't blame you for falling for C as the correct answer choice. It's imperative to look closely at the other answer choices and see how they stand against C. And when you do that you will see that option D stands taller than C when compared.
As per the question stem, there is no mention of the marketing company being used by the company. So, C is bringing in some new information that can be questioned as follows: What percentage of press coverage did the marketing company provide the drug company? Was it 100%? Or was it only a small number? Did majority of the public came to know about the drug through this marketing company or they came to know about it through other means, say, social media or drug company's own website? What if the marketing company came later into the picture and till then the drug company had already published the results of their new drug to the public via, lets say, there own public website/news paper/social media. So, even if the company that came into the picture late has a tainted reputation, it can not necessarily lead to a negative impact on the excitement surrounding the drug. You can say, it's a bit far fetched idea, but it is something that can certainly be a case.
For D, on the other hand, if the public comes to know about the results of the drug being short-lasting, that could seriously dampen the excitement.
Consider a case, where you read a news regarding some really cool gadget but then come to know that it lasts only two days, would you be as excited after hearing that? Certainly no! This is the reason why D outshines C and is the correct answer choice.