Which of the following taxpayers need not file a tax return for 2019?

1. Married taxpayers (ages 69 and 67 years), filing jointly, with gross income of $26,724.

2. An unmarried taxpayer who is over age 65, with gross income of $20,771.

3. An unmarried taxpayer, under age 65, with gross income of $26,058.

4. An unmarried taxpayer, over age 65, filing as head of household with gross income of $20,830.

5. All of the above taxpayers must file a return.