Here are the correct forms of the verbs for each sentence:

1. In 2001, the number of students who participated in the event **was** 1000.

2. Taxing private car owners **is** (or **can be**, depending on the context).

3. At 7 pm yesterday, my cousins **were watching** their favorite cartoon.

4. Everyone **is dancing** happily at the moment.

5. My younger brother promises that he **will drive** carefully next time.

1. In 2001, the number of students who participated in the event **was** 1000.

2. Taxing private car owners **is** (or **can be**, depending on the context).

3. At 7 pm yesterday, my cousins **were watching** their favorite cartoon.

4. Everyone **is dancing** happily at the moment.

5. My younger brother promises that he **will drive** carefully next time.

1. In 2001, the number of students who participated in the event **was** 1000.

2. Taxing private car owners **is** (or **can be**, depending on the context).

3. At 7 pm yesterday, my cousins **were watching** their favorite cartoon.

4. Everyone **is dancing** happily at the moment.

5. My younger brother promises that he **will drive** carefully next time.