In this sentence improvement question, choose the best alternative to replace the underlined preposition: London is one of the oldest towns of England.

Introduction / Context:
This question tests your understanding of prepositions used to show location in relation to countries and regions. When we talk about a city as belonging to or located inside a country, English prefers the preposition in rather than of. Exam questions often focus on this difference because many learners carry over patterns from their native language.

Given Data / Assumptions:
- Original sentence: London is one of the oldest towns of England. - Underlined preposition: of. - Options: in, at, besides, No improvement. - The intended meaning is that London is among the oldest towns located within England.

Concept / Approach:
The correct structure to express this idea is one of the oldest towns in England. We usually say in a country or in a region when we talk about geographical location. The preposition of is sometimes used with phrases like the capital of England, but that structure is different. Therefore, we must replace of with in to make the sentence grammatically and idiomatically correct.

Step-by-Step Solution:
Step 1: Identify that the phrase of England is attached to towns and describes where the towns are located. Step 2: Recall that for geographical location we use in: cities in India, villages in France. Step 3: Replace of with in to form one of the oldest towns in England. Step 4: Examine at, which is used for specific points or addresses, not for belonging to a country. Step 5: Examine besides, which means in addition to and does not fit the sentence at all. Step 6: No improvement cannot be chosen because of England is not the standard phrase here.

Verification / Alternative check:
Compare with other correct sentences: Paris is one of the largest cities in Europe or Jaipur is one of the most famous cities in Rajasthan. In each case, in is used to show that the city is a member of the group defined by the region. Using of in these examples would sound unusual or incorrect. In the same way, towns in England is the natural expression, confirming that in is the correct choice.

Why Other Options Are Wrong:
At in option B is used for specific locations (at the station, at the corner) rather than grouping towns within a country. Besides in option C means in addition to and does not express location or membership in a set. No improvement in option D is incorrect because of England is not the idiomatic preposition choice in this context.

Common Pitfalls:
Learners sometimes overuse of when talking about relationships, especially because phrases like the capital of England are correct. To avoid confusion, remember that when you list one item among many within a country or region, you normally say in that country or region. Keeping examples like one of the best schools in the city in mind will help you choose the correct preposition quickly.

Final Answer:
The correct sentence is London is one of the oldest towns in England, so the answer is in.