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Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

Scarlett is studying the neurology of mice. One article she reads suggests that the number of neurons a mouse has， N(t)， after t months is modeled by the function N(t)=N0*(1-r)^(t/τ)， where N0 is the initial number of neurons at time t=0， r is a rate where 0＜r＜1， and τ， measured in months， is a constant. If τ is 4 months， which of the following statements would best describe the relationship between the number of neurons and the number of months t that have passed since N0 was measured？