In English voice change, choose the correct passive form of the sentence: "We have finished the assignment."

Introduction / Context:
This question tests your understanding of active and passive voice, especially the present perfect tense. The given active sentence is "We have finished the assignment." You are asked to select the passive voice version that preserves the same tense and meaning. Voice change is a standard topic in English grammar exams and requires careful attention to helping verbs and past participle forms.

Given Data / Assumptions:

• Active voice sentence: "We have finished the assignment."
• Subject in active voice: "We".
• Object in active voice: "the assignment".
• Tense: present perfect, indicated by "have finished".
• We must keep the same time reference and sense in passive voice.

Concept / Approach:
To change a present perfect sentence from active to passive, we follow a systematic pattern. The object of the active sentence becomes the subject in the passive sentence. The passive structure for present perfect is: has or have + been + past participle of the main verb. The agent ("by us") is added if required. Therefore, "We have finished the assignment" should transform to "The assignment has been finished by us." Choosing the correct auxiliary verb (has or have) depends on the new subject in the passive sentence.

Step-by-Step Solution:
Step 1: Identify the verb tense in the active sentence. "Have finished" shows present perfect tense. Step 2: Identify the object in active voice that must become the subject in passive voice. The object is "the assignment". Step 3: Bring the object to the subject position, giving "The assignment ...". Step 4: Construct the passive auxiliary. Because "assignment" is singular, we use "has" rather than "have". Then follow the pattern: has + been + past participle. So we get "has been finished". Step 5: Add the agent if needed. The doer "we" becomes "by us" in the passive form. The full sentence becomes "The assignment has been finished by us." Step 6: Check for correct tense and agreement. The tense (present perfect) and meaning remain unchanged.

Verification / Alternative check:
We can verify by converting back from passive to active. Start with "The assignment has been finished by us." Bring "us" to subject position and change "has been finished" back to "have finished". The result is "We have finished the assignment", which matches the original sentence exactly. This confirms that the passive version is accurately formed. Also, compare with known patterns such as "They have completed the work" becoming "The work has been completed by them."

Why Other Options Are Wrong:
"The assignment were finished by us" is incorrect because "were" does not express present perfect; it expresses simple past or past continuous and also disagrees with the singular subject "assignment". "The assignment had been finished by us" is in the past perfect tense, not present perfect, and therefore changes the time reference. "The assignment has had been finished by us" is grammatically incorrect because "has had been" is not a standard verb sequence. "The assignment is finished by us now" is in the simple present passive and changes the tense and style. Only "The assignment has been finished by us" keeps the correct tense and meaning.

Common Pitfalls:
Learners often confuse present perfect with past perfect or simple present when forming passive structures, especially under time pressure. Another common error is choosing the wrong auxiliary verb for singular or plural subjects. Remember the formula for present perfect passive clearly: has or have + been + past participle. Also, do not add extra helping verbs like "had" where they are not needed. Practising transformations between active and passive forms across different tenses helps build accuracy.

Final Answer:
The correct passive voice form is "The assignment has been finished by us."