To solve this question, we need to choose the correct preposition to complete the sentence properly. Let's analyze the options and find the correct answer.
Option A: "Of"
This preposition is used to indicate a relationship or connection between two things. In this context, it means that the person being referred to possesses a similarity or resemblance to the boy the speaker knew at school.
Option B: "Off"
This preposition is used to indicate a separation or disconnection between two things. It does not fit the context of the sentence.
Since the sentence requires a preposition that shows a resemblance or similarity, the correct answer is Option A: "Of". It indicates that the person being addressed reminds the speaker of a boy the speaker knew at school.
So, the correct answer to complete the sentence is a. Of.

Understanding the Correct Usage: "Of" vs. "Off"
In the sentence "You remind me _________ a boy I was at school with," the correct option is "of." Let's break down why this is the case.
The Meaning of "Remind Me of"
- "Remind me of" is a phrase used to indicate that someone or something evokes memories or thoughts of another person or thing.
- In this context, "remind" functions as a verb that needs a preposition to connect it to the subject.
Why "Of" is Correct
- The preposition "of" is used to show relationships or connections between nouns.
- When you say "remind me of," you're establishing a connection between the current subject and the boy you remember from school.

Understanding "Off"
- The word "off" typically indicates separation, distance, or removal.
- For example, "take the book off the shelf" means to remove it from that location.
Common Usage and Examples
- "Remind me of" is commonly used in everyday English.
- Example: "This song reminds me of summer."
- "Off" does not fit in this context and would not convey the intended meaning.
Conclusion
Using "of" in the phrase "remind me of" helps clarify the relationship between the subject and the memory being referenced. Therefore, the sentence should be completed as "You remind me of a boy I was at school with."