some cancers are caused by mutations that stop certain proteins from working. the inactivation of what kind of protein could lead to cancer

Which of the following is true? species on earth today are but a fraction of all species that ever lived. the number of species existing at one time has decreased throughout history. extinctions of past species has happened gradually and on a small scale. most organisms present early in earth's prehistory were more complex than modern organisms. "bacteria represent a newer form of life, not present during the early prehistory of earth."