When variables compete to explain the same effects, what are they sometimes called?

Which of the following statements about the U.S. trade deficit is TRUE?

a. The U.S. trade deficit has steadily declined. b. The U.S. trade deficit has only negative economic impacts upon the American economy and consumer. c. The trade deficit is solely a result of the United States reducing tariffs thus allowing for more foreign goods to enter the American market. d. The fact that the U.S. dollar is a main international reserve currency helps to offset the negative economic impact of the trade deficit. e. All of these are true.

What are some of the potential effects of dual legitimacy in a presidential system?

What will be an ideal response?