Why did you waste best part of your life?
- A. Why the best part of your life wasted by you?
- B. Why were the best part of your life wasted by you?
- C. Why did the best part of your life wasted by you?
- D. Why was the best part of your life wasted by you?
Explanation
The simple past passive uses was or were plus the past participle wasted; the singular subject “best part” requires was. Hence, “Why was the best part ... wasted?” is correct.
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