The best answer to this question is Option A. This is an example of Congress using its enumerated powers. These are powers that are clearly stated in the Constitution. Since the Constitution explicitly says that Congress can regulate trade with foreign countries, and since a ban on elephant products is clearly a regulation of foreign trade, this is an enumerated power. Let us also look at why the other options are wrong.
Option B. Reserved powers: These are powers that are not given to any particular part of government by the Constitution. This is similar to Option E, because the 10th Amendment says that these powers (not given to the federal government or denied to the states) belong to the states. Since regulation of trade is specifically mentioned, it is not reserved.
Option C. Implied powers: These are powers that are not specifically listed in the Constitution but which are implied in the powers that are listed. The classic example of this is that the US government was allowed to create a National Bank even though the Constitution did not say it could. It was allowed to do that because the power to create a bank was implied in the power to make laws for the general welfare of the country. Option C is not the best answer because these are powers that are not clearly given to the government while the power to regulate foreign commerce is clearly given.
Option D. Concurrent powers: These are powers that both the state and the federal governments share. An example of this is the power to tax. The regulation of elephant products does not fall under this category because only the national government has the power to regulate foreign commerce.
For these reasons, Option A is the best answer.