Which renewable source of energy should the United States focus its research and development efforts to make this source of energy our country’s main energy source by the year 2050? Why?

Nuclear fission is utilised in the nuclear reactions. Research is still going on to develop techniques to harness the nuclear Fusion for electricity production. Although nuclear reactors are good source of energy but the materials used in the nuclear plants are non renewable(e.g radioactive elements). The disposal of radioactive materials produced during the Nuclear fission is not easy. So the states should focus on developing the solar energy as the main source of energy. Solar energy is renewable source and doesn't produce any waste products.

lockers 1, 4, 9, 16, 25, 40, and 49 are open

i ran through it by the other answer is wrong