Why Have Biologists Hypothesized That the First Land Plants Had

Why have biologists hypothesized that the first land plants had a low,sprawling growth habit?

A) At the time of the first land plants,the atmosphere had oxygen mainly close to the ground.
B) Land animals of that period consumed erect plants.
C) The ancestors of land plants,green algae,lack the structural support to stand erect in air.
D) Land animals of that period were small,so they needed short plants to eat.
E) Only fossilized plants exhibit this habit.