The correct answer to this question is the following.
Although there are no options attached we can say the following.
The main idea of the text "Election of Senators by Readworks," is the way Senators are elected to be a part of the legislative branch of the United States.
We know that each state of the Union has two Senators in the US Senate that have their headquarters in the Capitol, in Washington D.C.
They are elected for a 6-year term. Every two years, one-third of them are up to reelection.
The text also refers to independent candidates and how they can compete in elections. Senators are elected by direct vote. The candidate that receives the majority of the votes, wins.
Let's remember that the Senate is the upper chamber of Congress while the House of Representatives is the lower chamber of Congress. These are part of the legislative branch of the federal government. The other two branches are the executive branch or the President of the United States with his cabinet, and the judicial branch or the Supreme Court.