Answer:
Step-by-step explanation:
The correct sentences are:
I understood the story; it was easy.
Although I wanted to play, I sit at the table instead.
We will perform all the dances we learned last year.
The children were playing and the teachers are watching.
In the first sentence, the verb "understood" is correctly written in the past tense, as it refers to a past action. In the second sentence, the verb "sit" is correctly written in the present tense, as it refers to a current action. In the third sentence, the verb "will perform" is correctly written in the future tense, as it refers to a future action. In the fourth sentence, the verb "were playing" is correctly written in the past tense, while the verb "are watching" is correctly written in the present tense.