Final answer:
The early growth rate of Christianity is best described as exponential, with the number of adherents increasing rapidly in a pattern that sustained itself over time.
Step-by-step explanation:
The growth rate of Christianity in its early years cannot be accurately described by any of the static percentage options provided. Instead, the historical progression of Christianity is best characterized as exponential growth. Historians and scholars such as Rodney Stark have suggested that Christianity grew at an exponential rate, meaning it increased rapidly as the religion gained more adherents who then spread the faith further.
This type of growth reflects a rate that continually increases in proportion to the growing total number, which differs significantly from a steady percentage growth per year or decade. Such exponential growth is well-documented in various studies on the rise and expansion of Christianity in the first three centuries of the Common Era.