(2) No littering, spitting and planting trees can improve air quality and protect the environment.
(3) Fish live in water and breathe through gills. The water with dissolved oxygen enters from the fish mouth and flows out from the rear edge of gill cover, and the oxygen in the water enters the fish body through gill exchange. It can be seen that fish get oxygen from water through gills. Therefore, pollutants in the air do great harm to people and have little impact on fish. Another reason why fish can live in water is that they swim with their fins and move forward by swinging their tails and trunks.
(4) From the adaptive significance of behavior, animal behavior can be divided into feeding behavior, reproductive behavior, defensive behavior, aggressive behavior, migration behavior, social behavior and so on. From the way of behavior acquisition, animal behavior can be divided into innate behavior and learning behavior. Therefore, the behavior of students doing indoor exercises is a learning behavior from the way of acquisition.
So the answer is: (1) respirable particulate matter and sulfur dioxide;
(2) No littering, spitting and greening.
(3) gills; Swimming with fins;
(4) learning.