The correct answer is the following.
The four technologies that have helped America to develop into a powerful country are the invention of the automobile, the airplane, the railroad, and the telephone.
America has always been a country that produces many inventions that served as an important part of the U.S. advancements. A lot of money and talent have been invested in creating technologies that help people and the economy to grow. Important inventions such as the automobile changed completely the lives of the people, improving transportations and creating the new system of highways along the country. The railroad system in America also changed totally the transportation methods of goods. It opened the possibility to reach many new places and facilitated trade.
The invention of the airplane was a huge step for humanity that allowed the connection of people between countries in a much better, quickly and safer way. The telegraph and the telephone made possible communication between people around the globe and were the previous steps of the invention of the Internet.
