3. (D)
Question type: Explain a result
Although the question asks which statement is best supported by the argument, the argument itself clearly establishes a paradox or discrepancy: namely that the importation of mammoth ivory spiked in the period of time after African ivory was outlawed but then dipped again when a test for mammoth ivory was established. Instead, the expected result would be that there would be no change in the importation of mammoth ivory after the test was established. Answer choice (D) accurately resolves the paradox and explains the unexpected result.
(A) is irrelevant to the discrepancy presented.
(B) is irrelevant to the discrepancy presented.
(C) is irrelevant to the discrepancy presented.
(E) is irrelevant to the discrepancy presented.