Consider the following statements about objectivity and bias in historical writing:

1. Complete objectivity in historical research is often regarded as impossible due to the historian's inherent subjectivity.
2. Marxist historiography claims to be more objective because of its focus on class struggles as the core driving force of history.
3. The Annales School promoted a return to narrative history, opposing the trend of quantification in historical studies.
4. Post-modernist historians challenge the very idea of objective truth, arguing that all history is a subjective construct.

Which of the above statements are correct?