Which of the following best describes the us government?

Assuming your options are executive rule, dictatorship, direct democracy, and representative democracy, the correct answer is the last option - representative democracy.
It's not the executive rule, because the executive branch is not the only law-making branch in the US. It's not a dictatorship either, because the US doesn't have a dictator, but rather a president. It's not a direct democracy, because that would mean that people directly choose the laws themselves, which is not the case in the US, but was in ancient Greece, for example. Thus, the only correct answer is representative democracy, meaning that voters choose people to represent them and their wishes.