United States economy is considered by the Institute for Management Development to be the most competitive economy because A. of a high saving rate. B. of selected restrictions on imports from Japan and Europe. C. Americans are willing to work harder than anyone else is. D. of widespread entrepreneurship.

D. of widespread entrepreneurship.

Explanation:

Competitive economies are not characterized by imposing restrictions on foreign trade (option B) or necessarily saving more than anyone else (option A). Even the amount of hard working citizens is not a real measure, in some Asian countries people work for 16 hours per day and earn just a few a cents (option C). What makes an economy competitive is how many new innovations and how many new businesses appear every year. They don't even have to be made by Americans, but people living in America. E.g. Apple, Google, Tesla and many others were built by immigrants that found the opportunity to succeed in America.