When writing a critical essay, An essayist should analyze all the parts of the book. Option B is correct.
A critical essay is a form of academic writing which purpose is to analyze, interpret, and/or evaluate a text. In a critical essay, an author makes a claim regarding how particular ideas or themes are conveyed in a text, then supports that claim with evidence from primary and/or secondary sources.
The word "critical" of a critical essay simply means discerning and analytical since critical essays analyze and evaluate the meaning and significance of a text.