[R] Query about finding correlations

[lalitha viswanath]

Hi
I have a dataframe which has 3 columns of numeric data
A,B,C each of which has been obtained independent of
the other.

We are trying to find out, which of A or B cause C
i.e. We are hypothesising that C is the effect and
either A or B, not both is the cause.

i.e. A causes C and this cause-effect relationship
explains B.

The data for A contains more noise than that for B.
We are working with around 1000 points.

I would greatly appreciate any inputs on the best
statistcal approach to tackle this problem. 
I am thinking that we can find correlation
coefficients between A and C, and between B and C, but
I am not sure this answers the question.
Also we do not know whether the correlation between
them is linear or non linear.

Thanks
Lalitha