It Is True That When Using Concomitant Variation as Evidence

It is true that when using concomitant variation as evidence of a causal relationship between two variables

A) the technique can only be applied with quantitative variables.
B) we are looking for a one-to-one correspondence between the two variables and this is usually found.
C) when evidence of concomitant variation is found, the hypothesis is proved.
D) the absence of initial evidence of concomitant variation implies that there is no causation between the two variables.
E) there may be no causal relationship between variables even though there is initial evidence of concomitant variation.