Certain researchers have published peer-reviewed reports that the use of zinc lozenges reduces the length and severity of cold symptoms. Why are some scientists still skeptical about the merits of using zinc lozenges during a cold?

A) Most people get zinc in their diet so extra zinc lozenges may not affect a cold.
B) Ideas about vitamin C have been discredited, so zinc will also be ineffective.
C) There is no way of knowing if the original work was properly controlled.
D) There may be other reasons why the people taking zinc lozenges recovered faster.