单项选择题

American Government
The United States is a federal union of 50 states. The capital of national government is in Washington D. C. ( District of Columbia). The federal constitution sets up the structures of the national government and lists its powers and activities. The constitution gives Congress the authority to make laws which are necessary for the common defense and the good of the nation. It also gives the federal government the power to deal with national and international problems that involve more than one state. All powers that are not given to the federal government by the constitution are the responsibility of the individual states.
The federal government has three branches - the executive, the legislative, and the judicial. The legislative branch makes the laws, executive branch carries out the laws, and judicial branch interprets the laws. The President heads the executive branch and the Supreme Court heads the judicial branch. The legislative branch includes both houses of Congress—the Senate and the House of Representatives. The constitution limits the powers of each branch and prevents one branch from gaining too much power. For example, Congress can pass a Law the President may sign it. Nevertheless, the Supreme Court can declare the law unconstitutional and nullify it.
All government in the United States is" of the people, by the people and for the people". The people elect the President and the members of Congress. However, the President appoints the heads of federal departments and the Supreme Court judges. Every citizen votes in secret. Consequently, no one knows for whom and individual votes. The people believe that their government should provide a framework and order within which they are left free to run their own lives.
The main point of this passage is ______.