Paleontology is study of 

Paleontology is study of fossil plants and animals (both B and C).

In greek, 'paleos' mean ancient, 'ontos' mean life, and 'logy' mean study. hence the term paleontology refers to the study of ancient life forms.
We know that fossils are the preserved remains of plants and animals, which are the only means of proof of existence of ancient life. These fossils were studied to find out about ancient life forms like dinosaurs. Many new fossils are being discovered every now and then and their study continues to unravel the secrets of life from the past.