How can scientists ensure that their data are reliable?
by making a single observation
oby recording values without units
by keeping the results private
O by repeating trials during an experiment

answer:

The answer to your question is repeating trials during an experiment.

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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