Improvement of sentence: a part of the following sentence is considered incorrect. Choose the preposition that best improves the sentence. If no improvement is needed, choose the option marked No improvement. Please make it a point to send the letter at my address.

Introduction / Context:
This question checks your understanding of correct preposition use in English, especially with the noun address. Prepositions are small words like in, on, at, and to, but they seriously affect whether a sentence sounds natural and grammatically correct.

Given Data / Assumptions:

• Sentence given: Please make it a point to send the letter at my address.
• The focus is on the preposition before my address.
• Options include on, to, in, at, and No improvement.
• The intention is that the letter should reach the speaker's address.

Concept / Approach:
In English, we commonly say send the letter to my address or send the letter to me at this address. The basic pattern is send something to a person or place. The preposition to expresses direction or destination. At is used in some expressions like at this address, but in this exact sentence, to is needed before my address.

Step-by-Step Solution:
Step 1: Identify that the problem area is the phrase at my address. Step 2: Recall common collocations: send a letter to an address, send mail to a person. Step 3: Test each option: send the letter on my address, in my address, to my address, at my address. Step 4: Notice that only to my address sounds fully natural in standard English.

Verification / Alternative check:
You can also rephrase the sentence: Please send the letter to my home address. This clearly confirms that to is the correct preposition. Dictionaries and grammar books list examples like write to me, send an email to the office, and post the parcel to this address, which further supports the choice.

Why Other Options Are Wrong:

• on: We do not say send a letter on my address in standard English.
• in: In my address would refer to something written inside the address, which is not the intended meaning.
• at: Could work in a different structure like send the letter to me at this address, but not exactly as given.
• No improvement: Wrong because at my address is not the best form here.

Common Pitfalls:
Learners often transfer patterns from their first language and mix at and to. They may also remember phrases like meet me at this address and wrongly extend at to send the letter at my address. Always think about direction or destination; for sending and giving, the preposition to is normally required.

Final Answer:
Correct option: to.