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