A. Pluto was discovered in 1930.
Feedback The Passive Voice is formed according to this rule: Subject - Be+ Past Participle - Preposition 'BY' - Agent (who or what carries out the action). The right form for the Past Simple Passive is: was/were + past participle or verb+ -ed
B. Pluto is discovered in 1930.
C. Pluto has been discovered in 1930.
D. The discovery of Pluto was taken place in 1930.