In this sentence improvement item, you must choose the correct relative pronoun to complete a well known proverb. Original sentence: Uneasy lies the head which wears the crown.

Introduction / Context:
This question is based on a famous proverb that comments on the troubles of leadership. The correct traditional wording is Uneasy lies the head that wears the crown. The test checks whether you know the appropriate relative pronoun in this fixed expression and whether you can recognise the most standard form. Correct use of relative pronouns also reflects good grammar in complex sentences.

Given Data / Assumptions:

• The sentence talks about the head that wears the crown, a metaphor for a ruler or leader.
• The version given uses which as the relative pronoun.
• Options provide who, that, what, and no improvement.
• We assume that examination boards prefer the most idiomatic and widely accepted form of the proverb.

Concept / Approach:
In restrictive relative clauses referring to things or people, English often uses that. In traditional phrasing, the proverb uses that and appears in many literary and exam sources as Uneasy lies the head that wears the crown. While some might argue other pronouns are possible in normal sentences, in a fixed proverb the established form is what matters most. Therefore, substituting that for which gives the correct and recognised version.

Step-by-Step Solution:
Step 1: Recognise that the sentence is a proverb and recall its standard wording. Step 2: Note that the clause that wears the crown restricts and identifies which head is being talked about, so it is a defining relative clause. Step 3: Check option b, that, which matches the traditional version Uneasy lies the head that wears the crown. Step 4: Examine option a, who, and observe that although it may refer to persons, the grammatical subject here is head, a thing, not a person. Step 5: Examine option c, what, which does not function as a relative pronoun in this construction and would make the sentence wrong. Step 6: Consider option d, No improvement, and recall that examination keys usually require the well known form with that, not which. Step 7: Select that as the best improvement for accuracy and idiomatic use.

Verification / Alternative check:
You can verify by checking common references or remembering how you have seen this proverb in books and articles. Nearly all reliable sources phrase it as Uneasy lies the head that wears the crown. Changing that to which sounds less natural and less faithful to the established proverb. This confirms that that is the preferred relative pronoun here.

Why Other Options Are Wrong:
Who is wrong because the immediate antecedent is head, which is an inanimate noun, even though it symbolises a person. What is wrong since it cannot introduce a relative clause that specifies a noun in this way. No improvement is wrong because the given version with which does not reflect the standard proverb as taught and tested in English exams.

Common Pitfalls:
Students sometimes pick who because they think of the person wearing the crown rather than the head as the grammatical subject. Others may think that which is acceptable for things, forgetting that the proverb is traditionally fixed with that. In sentence improvement questions based on famous sayings, always try to recall the exact wording used in literature and exam materials.

Final Answer:
The improved sentence is Uneasy lies the head that wears the crown.