What must be true of a bill which has become law at a federal level?

It must have been signed by the president
It must be in the best interest of all Americans
It must have passed both the house and the senate***
It must have been introduced into the senate before the house.

Correct. The president's signature is usually required, but a presidential veto may be overridden by both houses of Congress.

So it is It must have passed both the house and the senate

Yes.

To determine what must be true of a bill that has become law at a federal level, you need to understand the process of how a bill becomes a law. Here are the steps:

1. Introduction: A bill is introduced in either the House of Representatives or the Senate.

2. Committee Review: The bill goes through a committee review process in the respective chamber where it was introduced. The committee may make changes, suggest amendments, or reject the bill.

3. Floor Debate: The bill is then presented to the full House or Senate for debate and voting. Amendments can be proposed during this stage.

4. Passage in One Chamber: If the bill receives a majority vote in one of the chambers (House or Senate), it moves to the other chamber.

5. Committee Review and Floor Debate in the Other Chamber: The bill goes through a similar process of committee review and floor debate in the other chamber. Again, amendments can be proposed.

6. Conference Committee: If both chambers pass versions of the bill with differing details, a conference committee is formed to reconcile the differences. The committee members negotiate and reach a compromise.

7. Final Passage: After the conference committee finalizes the bill, it is voted on again by both chambers. If it receives a majority vote in both chambers, it moves on.

8. Presidential Approval: The bill is sent to the President for approval. The President can either sign the bill into law or veto it. If the President signs the bill, it becomes law. However, if the President vetoes it, the bill can still become law if both chambers of Congress override the veto with a two-thirds majority vote in favor.

Based on this process, the following statement is true about a bill that has become law at a federal level:
- It must have passed both the House of Representatives and the Senate.

The other statements presented in the question are not necessarily true for a bill to become law. While it is common for the President to sign a bill into law, it is not mandatory. Additionally, the bill does not need to be in the best interest of all Americans, as different bills may have different impacts on various groups of people. Finally, there is no strict requirement that a bill must be introduced into the Senate before the House. Bills can be introduced in either chamber and go through the legislative process described above.