"Biorock technology" is talked about inwhich one of the following situations?

1. A

   Restoration of damaged coral reefs

   Restoration of damaged coral reefs. Biorock / mineral accretion grows limestone on steel under low voltage.

2. B

   Development of building materials using plant residues

   Plant-residue building materials. Different tech.

3. C

   Identification of areas for exploration/extraction of shale gas

   Shale-gas exploration. Unrelated.

4. 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).