In the following sentence, the bracketed part is incorrect. Choose the option that best improves the bracketed part so that the sentence is grammatically correct. I (didn't see) him since we met two years ago.

Introduction / Context:
This sentence improvement question tests your understanding of present perfect tense in English, especially when used with since and a specific time reference in the past. The sentence describes an action that has not happened from a point in the past up to the present. You must choose the option that correctly expresses this continuous period of non occurrence.

Given Data / Assumptions:
- Original sentence: I (didn't see) him since we met two years ago. - Options: am not seeing, have not seen, had not seen, No improvement. - The meeting happened two years ago, and from that time until now the speaker has not seen him.

Concept / Approach:
When we talk about a situation that started in the past and continues up to the present, especially with since and a definite past time, English normally uses the present perfect tense. The pattern is have or has plus past participle. Therefore, the correct form for this context is I have not seen him since we met two years ago. The simple past did not see would suggest a finished action in the past, not a state continuing up to now, and so it is not appropriate with since in this meaning.

Step-by-Step Solution:
Step 1: Identify the time structure: since we met two years ago clearly indicates a starting point in the past from which the non seeing continues to the present. Step 2: Recall the rule: present perfect (have or has plus past participle) is used for actions or states that began in the past and continue up to now, often with since or for. Step 3: Test have not seen. I have not seen him since we met two years ago correctly expresses that the speaker still has not seen him up to the present moment. Step 4: Test am not seeing. I am not seeing him since we met two years ago is ungrammatical, because present continuous does not combine naturally with since in this pattern. Step 5: Test had not seen. I had not seen him since we met two years ago would require another past reference point to make sense in past perfect and is therefore not correct in isolation. Step 6: No improvement is wrong because did not see does not match the ongoing time relationship expressed by since.

Verification / Alternative check:
Compare with similar structures: I have not spoken to her since last year and He has not visited us since he moved abroad are both standard usages of present perfect with since. Replacing the present perfect in these sentences with simple past would distort the meaning and suggest something different. In the same way, I did not see him since we met two years ago sounds incorrect to native speakers. The correct form, I have not seen him since we met two years ago, fits the well established pattern.

Why Other Options Are Wrong:
Am not seeing is wrong because present continuous describes actions happening right now or around the present, not a long period from a past point until now. Had not seen is wrong because past perfect is used to relate two past times, and here the sentence is clearly anchored to the present. No improvement is wrong because did not see conflicts with the use of since to mean from that time up to now.

Common Pitfalls:
Many learners are tempted to use simple past in all negative statements, especially after the subject I. However, time expressions like since two years ago and since we met demand present perfect if we want to include the present moment. A quick check is to ask whether the situation is still true now. If it is, present perfect is usually the right choice. Practising with pairs like I did not see him yesterday versus I have not seen him since yesterday will help you choose correctly in exams.

Final Answer:
The correct improvement is: I have not seen him since we met two years ago.