单项选择题

Life on land probably began about 430 million years ago, though it has existed in the water for perhaps as long as 3, 000 mil lion years. When we think of the first life on land, we probably think of strange animals coming out of the oceans, but, in fact, no animals could have been living if plants had not been on land first. Plants had to be on land before animals arrived. They supplied the first land animals with food necessary to live, since they are the only form of life that is able to get and store energy.
The first plants to exist out of the water were probably certain kinds of algae(海藻) which were followed by other plants that grew close to the ground near water and needed water in which to repro duce. Once the move to land had been made, however, evolution (进化) took place quickly. By the end of 100 million years, plants had developed their roots, and some developed tall tree like forms, since height was very important in competing for sunlight. About 300 million years ago, much of the world was covered with forests of huge trees. In most ways they were like modern trees. They had roots, leaves, wood, but mostly they had not developed seeds.

According to the passage, the higher a tree grows,（）

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