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OG-2
Passage 24
A tall tree can transport a hundred gallons of water a day from its roots deep underground to the treetop. Is this movement propelled by pulling the water from above or pushing it from below? The pull mechanism has long been favored by most scientists. First proposed in the late 1800s, the theory relies on a property of water not commonly associated with fluids: its tensile strength. Instead of making a clean break, water evaporating from treetops tugs on the remaining water molecules, with that tug extending from molecule to molecule all the way down to the roots. The tree itself does not actually push or pull; all the energy for lifting water comes from the sun’s evaporative power.
1. Which of the following statements is supported by the passage?
A. The pull theory is not universally accepted by scientists.
B. The pull theory depends on one of water’s physical properties.
C. The pull theory originated earlier than did the push theory.
2. The passage provides information on each of the following EXCEPT
A. when the pull theory originated
B. the amount of water a tall tree can transport
C. the significance of water’s tensile strength in the pull theory
D. the role of the sun in the pull theory
E. the mechanism underlying water’s tensile strength
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