Carbon dioxide. Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 60% higher than that of air (1.225 g/L) that is odorless at normally encountered concentrations. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms.
You should only do ballet in pregnancy if you are used to it. Ballet stretches can place a lot of pressure on your joints, especially your pelvic joints, and standing on one leg can cause pain in your pelvis.
Swimming is just about as good as it gets for a total workout. If you are pregnant, the buoyancy of the water will take stress off your joints. If you swam before you became pregnant, you will likely be able to continue swimming unless you have a problem with your pregnancy.