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Considering that she does not know the population standard deviation, the hypothesis test that she should use is given by:
c. one-sample, left-tailed t-test for a mean.
First, we consider that she does not know the population standard deviation, hence a t-test should be used instead of a z-test.
Then, we consider that she suspects that the mean weight is less than 15 lb, and less is associated with a left-tailed test, instead of a right-tailed(associated with more) or a two-tailed(associated with different).
Hence option c is correct.
More can be learned about an hypothesis test at https://brainly.com/question/26454209