Outcome Pretreatment Posttreatment Time C1 shows the average outcome of the control group before the treatment T1 shows the average outcome of the treatment group before the treatment C2 shows the average outcome of the control group after the treatment T2 shows the average outcome of the treatment group after the treatment B shows the average outcome of the treatment group ifthere would have been no treatment (in the absence ot the treatment) a) In this graph, what is the average causal effect of the treatment? (max 1 sentence) b) In this graph, what ist he differenceindifference estimator ofthe effect of the treatment? (max 1 sentence) (Hint: use the letters shown in the gaph in your answers for a) and b)) c) What is the name of the curcial assumption for differnces-in-differnces estimation (as discussed in the lecture)