Determining reaction formula from optical absorption graphs
Let's see. You are right in that it can't be (a). Now consider (c): A and B are consumed, while F and G accumulate. Where is that intermediate that goes up, then down?

As for (d), I believe there is no way we can tell that from (b) based on the picture alone, without looking at the numbers. See, suppose $\lambda_1$ actually measures B, and A is in huge excess; what would be the qualitative difference between the two? I can't see any.