Earth has several ideal features which enable it to support life. most important is the
a) gravitational force on earth.
b) existence of tectonic plates.
c) relationship between earth and its moon.
d) existence and amount of water on earth's surface.

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

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