In this grammar improvement question, choose the option that best replaces the bracketed part of the sentence so that it reads correctly: She (starts walks) without responding.

Introduction / Context:
This question tests understanding of tense consistency and correct verb phrase formation in English. The original sentence is She starts walks without responding, where the bracketed part is ungrammatical. In competitive exams, such questions frequently require the learner to choose the verb form that fits both the tense and the structure of the sentence. Correct handling of tenses is crucial for clear written and spoken communication.

Given Data / Assumptions:
The important elements in the question are as follows:

• Original sentence: She starts walks without responding.
• The focus is on replacing the incorrect verb group starts walks.
• We must choose an option that fits naturally into She ... without responding.
• There is no explicit time marker like yesterday or every day, but the structure suggests a simple narrative past.

Concept / Approach:
The phrase starts walks is incorrect because it tries to join two main verbs without any auxiliary or gerund structure. A natural English sentence here would use a single past tense verb phrase such as started walking. This makes the action complete and consistent with a narrative style. We therefore look for an option that gives a simple past continuous sense of action in progress at that moment. Among the given options, started walking fits best as a simple past verb followed by a gerund, which together form a smooth and grammatically correct expression.

Step-by-Step Solution:
Step 1: Observe that starts walks is ungrammatical. Two main verbs cannot stand side by side in this way. Step 2: Consider She started walking without responding. This is a natural and correct way to describe an action that began in the past. Step 3: Check option a, started walking. If we insert it, the sentence becomes She started walking without responding, which is correct and clear. Step 4: Check option b, had started walking. This would give She had started walking without responding, which is also grammatically possible but suggests a more complex past perfect context that is not necessary here. Step 5: Check option c, starts walking. She starts walking without responding is present tense and could be correct in some contexts, but exam sentences of this type are usually in simple narrative past. Step 6: Option d, no improvement, cannot be correct because the original phrase is clearly wrong. Step 7: Select option a as the best and simplest improvement.

Verification / Alternative check:
A quick check is to read the sentence aloud with each option. She started walking without responding sounds smooth and complete. She had started walking without responding suggests that another action in the past will follow, making it slightly more complex than needed. She starts walking without responding is acceptable only in a present tense narrative but does not match the typical exam pattern here. Since exam questions usually aim for the simplest correct structure, started walking is the most appropriate choice.

Why Other Options Are Wrong:
Option b (had started walking) is grammatically correct but implies a past perfect time frame that is not indicated anywhere in the sentence. Option c (starts walking) is in the present tense and may not fit the narrative style implied. Option d (no improvement) is definitely wrong because starts walks is never correct in standard English. Therefore these options do not provide the best improvement for the bracketed part.

Common Pitfalls:
Many learners either ignore tense consistency or think that more complex tenses such as the past perfect are always superior. Another common error is not noticing that two verbs are standing side by side without a proper structure, for example starts walks instead of started walking. To avoid such mistakes, learners should focus on simple, clear tense choices and ensure that verb groups follow standard patterns such as verb in past form plus verb plus ing when forming a progressive action phrase.

Final Answer:
The correct improvement is started walking, so the sentence becomes She started walking without responding.