Select the correct passive form of the given sentence:

The marine biologists, after months of oceanic surveys, have discovered a rare deep-sea species.

The correct answer is: A rare deep-sea species has been discovered by the marine biologists after months of oceanic surveys.

Step-by-Step Explanation:

1. Analyze the original sentence:
- Subject: The marine biologists
- Verb (Active Voice): have discovered (Present Perfect Tense)
- Object: a rare deep-sea species
- Adverbial/Prepositional phrase: after months of oceanic surveys

2. Apply the Active to Passive conversion rule for Present Perfect Tense:
- Active voice structure: Subject + has/have + V3 (past participle) + Object
- Passive voice structure: Object + has/have + been + V3 (past participle) + by + Subject

3. Form the passive sentence:
- Make the original object ("A rare deep-sea species") the new subject.
- Since "a rare deep-sea species" is singular, select the singular auxiliary verb has (instead of have), followed by been discovered.
- Include the agent preceded by "by": by the marine biologists.
- Retain the phrase after months of oceanic surveys in its natural position.

Combining these elements gives:
"A rare deep-sea species has been discovered by the marine biologists after months of oceanic surveys."