Choose all correct \"TRUE" statements. (a) The main reason why we cannot obtain the causal effect from simply mnning linear regression on observational data is that Yi and 51' are correlated in the causal equation Yi:O+1Xi+ai. (b) If XE is randomly assigned through experiments then we can include other characteristic variables and still estimate the same causal effect. (c) Statistical experiments help us understand the deductive mechanism through which X causes Y. (d) Eliminating spurious correlation is critical in causal inference but not so in predictionl