It would be wrong to conclude that a person has a Streptococcus infection if there is no other evidence than the fact...

I guess, the logic structure of the stimulus is like the following: "Only the fact S bacilli are present(A) ===> S infection(B)" is wrong Because, "S infection(B) ===>the host is physically run down(C)" The logic of the stimuli (B) is: "Only(on the basis alone) receiving 6 or more hours...(A) ===> bloom(B)" is wrong Because, "To bloom(B) ===> both 6 or mores(A) & alkaline soil(C)" In short, A===>B is wrong Because, B ==> C & A. Is this logic structure same as the one of the stimulus( A===>B is wrong because B===> C) ?? I totally understand the stimuli(B) is the closest than others though. Please, help me out.