why is D right

The flaw in this argument hinges on the word "reported." We are told that 5 years ago 5% of reported cases resulted in death, but today 18% of reported cases end in death. The argument then concludes that the disease has become more deadly. However, the argument draws that conclusion on the basis of only partial data- sure some cases are not being reported. Let's imagine that 5 years ago there were 100 reported cases, and 5 deaths leaving a death rate of 5%. Today, however, farmers have stopped reporting the mild cases, and only report 25 severe cases, with 5 deaths, leading to a reported death rate of 20%. However, the disease did not become more deadly, rather farmers are underreporting the number of total cases making the death rate appear higher than it actually is. It doesnt change the percentage, it casts doubt on its accuracy.