Correct option is C
• The given sentence is in present continuous active voice.
• Rule for passive voice:
Active: Subject + is/are + verb+ing + object
Passive: Object + is/are being + past participle + by + subject
• Apply:
Crows are chasing away cuckoos →
Cuckoos are being chased away by crows
Meanings of other options:
• (A) Wrong tense (past continuous)
• (B) Incorrect verb form
• (D) Simple present, not continuous