Думаю, что так :)
1.1. She's writing a letter.
1.2. They are watching TV.
1.3. He's waiting at the bus stop.
1.4. He's skateboarding.
1.5. We are doing an exam.
1.6. I am swimming.
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2.1. She isn't writing a letter.
2.2. They aren't watching TV.
2.3. He isn't waiting at the bus stop.
2.4. He isn't skateboarding.
2.5. We aren't doing an exam.
2.6. I am not swimming.