Beavers, large members of the rodent family in North America, are often referred to as “ecosystem/keystone engineers” by wildlife managers. Ecosystem engineers are described as animals that create, alter, or destroy a habitat. Beavers contribute to river ecosystems by bringing down old and dead trees along riverbanks. They use these trees to make their dams. Although these dams are primarily used for protection and food storage, scientists report that these dams change the surrounding environment in different ways. Given this information, in three to five sentences, describe a potential benefit that beavers contribute to the ecosystem as keystone engineers and describe a plausible impact that the removal of beavers could have on the surrounding ecosystem.

b) mutualism

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the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.