In this sentence improvement item, choose the correct form to replace the bracketed part: "What would the cavalry (doing) out here?"

Introduction / Context:
This question tests your understanding of verb forms used with modal verbs in English. The sentence "What would the cavalry doing out here?" sounds awkward because the verb form after the modal "would" is not correct. Exams often present such slightly incorrect sentences and ask you to replace a bracketed part with a grammatically accurate alternative that still preserves the intended meaning.

Given Data / Assumptions:

• The original sentence is "What would the cavalry (doing) out here?"
• The subject is "the cavalry", which is treated as a singular collective noun in this context.
• The modal auxiliary is "would".
• The speaker is probably expressing surprise about the possible activity of the cavalry at some place.

Concept / Approach:
With modal auxiliaries like "would", "could", "might", and "should", the standard pattern is modal + be + present participle when we want to talk about a continuous action. For example, "What would they be doing?", "Where could she be going?", or "Why might he be waiting?" In our sentence, the correct pattern is "would be doing". The given bracketed word "doing" alone is not enough; it must be combined with "be" to form the appropriate progressive construction after the modal verb.

Step-by-Step Solution:
Step 1: Identify the modal verb "would" in the sentence.Step 2: Recall the structure for progressive aspect with modals: would + be + verb in ing form.Step 3: Recognise that the intended meaning is to ask what activity the cavalry might be engaged in at that location.Step 4: Among the options, pick the one that completes this pattern, namely "be doing".Step 5: Rebuild the full sentence as "What would the cavalry be doing out here?" and confirm that it now sounds natural and grammatically correct.

Verification / Alternative check:
Test the other options in the full sentence. "What would the cavalry be done out here?" is wrong because "be done" is passive and does not fit the sense of cavalry performing an action. "What would the cavalry done out here?" is ungrammatical. Leaving the sentence as "What would the cavalry doing out here?" is also not acceptable in standard English. In contrast, "What would the cavalry be doing out here?" matches patterns found in native usage and grammar references.

Why Other Options Are Wrong:

• Option B "be done" would produce a passive construction that is not suitable when the cavalry is the agent performing an action.
• Option C "done" alone cannot follow the modal verb "would" in this context; we need either the base form or a continuous structure.
• Option D "no improvement" keeps the incorrect pattern "would the cavalry doing", which is ungrammatical.

Common Pitfalls:
Many learners forget that modals like "would" are followed by a bare infinitive such as "do" or by "be doing" when describing a continuous action. Mixing the ing form directly with a modal without "be" creates errors. Whenever you see a modal plus an ing form, check whether "be" is missing from the structure.

Final Answer:
The correct improvement is "What would the cavalry be doing out here?", so the best replacement is "be doing".