The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
Some of the powers of the Legislative Branch are the power to create laws that benefit the United States, the power to declare war, the power to raise money through taxation and give it to the government offices, the power to ratify foreign treaties, the power to approve the nominations made by the President of the United States, and the power to impeach the President and other government officials.
I believe the most important powers are the power to create laws that benefit the United States, the power to declare war, the power to raise money through taxation because legislation is the laws that rule the country, the President cannot decide to go to war until Congress support it or denies the declaration, and expert committees in Congress have the knowledge to give the money for the government to function.