A
Restoration of damaged coral reefs
B
Development of building materials using plant residues
C
Identification of areas for exploration/extraction of shale gas
D
Providing salt licks for wild animals in forest/protected areas
Correct answer: (a) Restoration of damaged coral reefs
Explanation
- A
Restoration of damaged coral reefs
Restoration of damaged coral reefs. Biorock / mineral accretion grows limestone on steel under low voltage.
- B
Development of building materials using plant residues
Plant-residue building materials. Different tech.
- C
Identification of areas for exploration/extraction of shale gas
Shale-gas exploration. Unrelated.
- D
Providing salt licks for wild animals in forest/protected areas
Salt licks. Unrelated.
Summary. Official key is (a). Biorock (mineral accretion) uses a small current on a conducting frame so calcium carbonate precipitates — a coral-reef restoration method (Goreau / Hilbertz).