1. The correct alternative for the first sentence is option a) didn't-was. The correct sentence would be "He didn't swim in the lake. It was too cold." This means that he chose not to swim in the lake because the water was too cold.
2. The correct alternative for the second sentence is option b) were-were. The correct sentence would be "We were at the cinema yesterday. The film was exciting." This means that they were at the cinema yesterday and the film they watched was exciting.
3. The correct alternative for the third sentence is option c) was-did. The correct sentence would be "A: Where were you born? B: I was born in Manchester." This means that the person being asked was born in Manchester.
4. The correct alternative for the fourth sentence is option a) did-didn't. The correct sentence would be "A: Did you finish the novel? B: No, I didn't. It was boring." This means that the person being asked did not finish the novel because they found it boring.
5. The correct alternative for the fifth sentence is option b) didn't-didn't. The correct sentence would be "Janet didn't have breakfast." This means that Janet chose not to have breakfast.
6. The correct alternative for the sixth sentence is option a) was-wasn't. The correct sentence would be "B: No, it wasn't American. It was German." This means that the person being asked clarifies that their car was not American, but instead, it was German.
7. The correct alternative for the seventh sentence is option b) was-were. The correct sentence would be "My classmates were with me." This means that the person being asked was accompanied by their classmates on the boat.
8. The correct alternative for the eighth sentence is option a) did. The correct sentence would be "Did you see my book? I can't find it." This means that the person is asking if the other person saw their book because they cannot find it.