TOEFL Listening: ETS-TOEFL听力机经 - 68N3H3133M1NE1DDP$

According to the ejection theory, why do some stellar embryos stop growing before they become stars? A. The motion of dust and gas inhibits their growth. B. The cores in which they form are not dense enough. C. They start forming in the area of a molecular cloud with the least amount of material. D. They are moved by gravitational forces to areas outside cores.