Complete the statement: If AB, CD, then
a. AB - CD
b. AB = CD
C. ABCD
d. AB - CD
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What situation is an example of an observational study

Anyone know? will mark brainliest if correct

David estimated he had about 20 fish in his pond. a year later, there were about 1.5 times as many fish. the year after that, the number of fish increased by a factor of 1.5 again. the number of fish is modeled by f(x)=20(1.5)^x. create a question you could ask that could be answered only by graphing or using a logarithm.