The answer would be "Estoy escribiendo" because estan means they are, esta means he is, and estamos means we are, adn we are talking about something in first person and estoy means I am so this perfectly fits it
Hope this helps
Answers:
1. Escribir
2. Andar en bicicleta
3. Nadar
4. Cantar
5. Esquiar
6. Andar en patineta
