The lengthening of a transmitted signal's wavelength and/or a decrease in its frequency, which indicates that the object is moving away from the observer, is called the
a) spectrum.
b) red shift.
c) blue shift.
d) distortion.

i think it is true since you can test the answer and can use observations to complete it.

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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