how to choose correct OA?

NSNguyen wrote:Taken together, some 2,000 stocks recommended on a popular television show over the course of the past 12 years by the show’s guests, most of whom are successful consultants for multibillion-dollar stock portfolios, performed less successfully than the market as a whole for this 12-year period. So clearly, no one should ever follow any recommendation by these so-called experts.
Each of the following, if true, weakens the argument EXCEPT:
(A) Taken together, the stocks recommended on the television show performed better than the market as a whole for the past year.
(B) Taken together, the stocks recommended on the television show performed better for the past 12-year period than stock portfolios that were actually selected by any other means.
(C) Performance of the stocks recommended on the television show was measured by stock dividends, whereas the performance of the market as a whole was measured by change in share value.
(D) Performance of the stocks recommended on the television show was measured independently by a number of analysts, and the results of the all the measurements concurred.
(E) The stock portfolios for which the guests were consultants performed better for the past 12-year period than the market as a whole.

pinktiger wrote:I pick D.

Torn between c and d though. But D seems neutral and doesn't weaken the argument.

Any body why C is incorrect?