What are the three main groups into which mammals are divided?

Would really appreciate it, i have an idea but not completely sure

Photosynthesis uses co2 and cellular respiration produces co2. we call the point when the two processes are in balance--when there is no net production of co2--the compensation point. how might you limit one of the processes in order to achieve a compensation point?

Hemoglobin is a proton that carries oxygen around your body what is hemoglobin made from