Why Would Astronomers Have Difficulty Spotting a Large Incoming Asteroid

Why would astronomers have difficulty spotting a large incoming asteroid headed for Earth?

A) It remains in a fixed position in the sky as it comes in directly, so astronomers cannot see its trajectory.
B) It comes in so fast that they do not have time to see it.
C) It is dark before becoming heated in Earth's atmosphere.
D) It is not an important topic to monitor for most astronomers.
E) It is simply too big to seem as if it is moving.