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 carbon dioxide,which is necessary for photosynthesis,was primarily located close to the ground.
B) They were tied to the water for reproduction and thus needed to remain in close contact with the moist soil.
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) There was less competition for space;only once land plants spread out did they start to grow upright.