The correct answer is C.
The sentence “I will complete my project next week” is in the active voice. This means that the subject of the sentence (I) is doing the action (completing the project). The passive voice is used when the focus is on the action, not the person doing the action. In the passive voice, the subject of the sentence is acted upon by the verb. In this case, the project is being completed by me.
A. Next week my project I will complete.
This sentence is in the active voice, but it is not grammatically correct. The subject (I) and the verb (complete) are not in the correct order.
B. My project will be completed by me next week.
This sentence is in the passive voice and is grammatically correct. However, it is not as concise as C.
D. Next week my project will be completed.
This sentence is in the passive voice and is grammatically correct. It is also concise, but it does not specify who will be completing the project.