In this sentence improvement item, choose the correct verb form to replace the bracketed phrase "(have done)" in the sentence "I have done my exercises when Keshav came to see me."

Introduction / Context:
This question tests your understanding of past perfect tense in a narrative about two events in the past. The sentence describes a situation where a person completed their exercises before Keshav arrived. To show clearly which action happened first, English uses the past perfect tense for the earlier action and simple past for the later one. The bracketed verb phrase "have done" does not match this pattern when combined with "came".

Given Data / Assumptions:

• Earlier action: finishing exercises.
• Later action: Keshav came to see the speaker.
• Bracketed phrase: "have done".
• Options: "had done", "done", "doing", "No improvement".

Concept / Approach:
When two actions in the past are related and one clearly happened before the other, the earlier action is often expressed in past perfect tense using "had" plus past participle. The later action takes simple past. In this case, the exercises were completed before Keshav arrived, so the correct structure is "I had done my exercises when Keshav came to see me". The present perfect "have done" is used when there is a connection to the present, which is not the case here because both events are in the past.

Step-by-Step Solution:
Step 1: Identify the time of each action: doing exercises first, Keshav coming afterward. Step 2: Notice that the verb "came" is in simple past. Step 3: Apply the rule for sequencing: use past perfect "had done" for the earlier completed action. Step 4: Replace "have done" with "had done" to get "I had done my exercises when Keshav came to see me". Step 5: Check that the sentence now clearly shows the order of events.

Verification / Alternative check:
Read the improved sentence slowly: the reader first understands that the exercises were already complete and then sees that Keshav arrived. If you keep "have done", you mix present perfect with simple past, which is not standard when both actions are clearly in the past. The options "done" and "doing" on their own are grammatically incomplete or incorrect in this position. Only "had done" fits the correct tense sequence used in exam level English.

Why Other Options Are Wrong:
"Done" alone would require an auxiliary verb such as "have", and on its own it does not form a complete predicate here.

"Doing" is a present participle and would lead to a different structure like "I was doing my exercises when Keshav came", which changes the meaning.

"No improvement" keeps "have done", which improperly mixes present perfect with a clearly past time reference in the same clause pair.

Common Pitfalls:
A common mistake is to overuse present perfect because it looks sophisticated. However, present perfect is best reserved for situations that link past actions with the present. When describing a sequence of past events, especially in stories or reports, always check whether one action happened before another. If it did, consider using past perfect for the earlier action, as in "had finished", "had left", or "had done".

Final Answer:
The correct improvement is "had done", giving the sentence "I had done my exercises when Keshav came to see me".