Answer Choice A Confusion

Hi! Can you please explain why answer choice A is not LM->CD ? I was following the because format that the passage gave, but it says that this answer choice is CD->LM? My thinking was carbon dioxide is necessary for the limewater to turn milky ... ? Does "because" introduce S or N consistently or does it depend on the question? Also, it talked about causal relationships-will we learn more about the difference between S &N and cause and effect at some point? Thank you so much!