Akind of variable that a researcher purposely changes in an investigation is

Which of the following best describes internal energy? a. the difference between the kinetic and potential energies of the particles in a system b. the sum of the kinetic and potential energies of the particles in a system c. the sum of the kinetic and thermal energies of the particles in a system d. the difference between the kinetic and thermal energies of the particles in a system

First to answer will be the brainliest i need the answer asap

How long will a plane have to fly continuously with 1100 miles per hour in order to cover the same distance as that from earth to the next star, proxima centauri?