Where Does Most of Earth's ¹⁴C Come From

Where does most of Earth's ¹⁴C come from?

A) It is continually being formed as a result of the photosynthesis process
B) It is continually being formed by the impact of cosmic rays on the atmosphere.
C) It comes to Earth from outer space along with other cosmic rays.
D) It was deposited on Earth when the solar system first evolved.
E) It was deposited on Earth many years ago by meteors.