1. 과제가 수행되었다 = The task has been performed/done. (과제 = assigned work, task - usually not a routine one) 2. 임무가 완료됐다 = The mission has been accomplished. (임무 = mission, assigned duty) 3. 작업이 완료됐다 = The job/work has been finished. (작업 = (usually physical) job; routine work or operation) 과제, 임무, 작업 are all fairly common words used in different contexts. 수행되다(be performed, be done) and 완료되다(be completed, be finished) are in passive voice. In Korean, active voice is preferred when both can be use. The sentences can be rewritten using active voice as follows. 1. 과제를 수행했다. (= 과제를 끝냈다) 2. 임무를 완료[완수]했다. (= 임무를 끝냈다, 임무를 다했다). 3. 작업을 완료했다. (= 작업을 끝냈다, 작업을 다 했다) 수행, 완료, 완수 are relatively formal words. The equivalent expressions in parentheses are used more often in casual conversation.

보통 과제가 끝났다 작업이 끝났다 이런 표현이 더 자연스러워요 '수행되었다,완료됐다' 이런 표현을 쓰면 조금 어색해요 딱딱하고