Answer:
active
Explanation:
The sentence is in present perfect tense.
For active voice, it is subject + have/has + verb + object.
They have found the missing ring.
↓ ↓ ↓ ↓
subject have verb object
Passive voice would be object + have/has been + verb.
The ring has been found by them.
↓ ↓ ↓ ↓
object has been verb subject
Hope that helps.
