Answer :
Hmm, it seems like the word that signals cause and affect is "Since". The reason I say this is because that is the reason (the cause) and the affect is rescheduling the lunch. (the effect). Good luck, do you understand?
Answer:
Since Robin has to work this Saturday, would you like to reschedule our lunch?
Explanation:
This sentence says that Robin has to work on Saturday. As a result, or effect, lunch may have to be rescheduled.