Consider the following statements regarding historical criticism and analysis of sources:

1. External criticism is used to verify the authenticity of the source material itself.
2. Internal criticism focuses on examining the credibility and reliability of the source’s content.
3. Historical criticism is only relevant to primary sources, as secondary sources do not require scrutiny.
4. Synthesizing data from various sources allows historians to form a well-rounded view of historical events.

Which of the statements are correct?