Correct Answer:
C. will have completed
The question asks for the correct future perfect tense. The Future Perfect tense is used to describe an action that will be completed before a specific point in the future. Its structure is "will have + past participle." The phrase "by the end of this month" clearly indicates a future deadline or a point in time by which the action will be finished.
- The correct answer is C: "will have completed." This correctly forms the Future Perfect tense. It signifies that the action of "completing the project" will be finished at or before the specified future time, "by the end of this month."
- A: "completed" is the Simple Past tense. This refers to an action that has already finished, which contradicts the future time marker "by the end of this month."
- B: "will complete" is the Simple Future tense. While it indicates a future action, it doesn't convey the idea of completion *before* a specific future point, which is crucial for the Future Perfect. It simply states they *will* do it, not that it *will be done by* a certain time.
- D: "complete" is the base form of the verb or Simple Present tense (for plural subjects). It is used for habitual actions or facts, not for future actions completed by a deadline.
Therefore, "will have completed" is the only option that accurately expresses an action finished before a future deadline.