Answer: A) has rung.
Explanation: a participle is a word formed from a verb but used as an adjective or a noun. A participle can also be used to make compound verb forms, for example to form a past perfect or present perfect which is formed using the verb "have" in present (present perfect) or past (past perfect) and adding the past participle of the main verb. In the given sentence the main verb is "ring" which in past participle is "rung" so the correct answer is "He has rung the same bell for the past 50 years."
