Consider the following activities : 1. Spreading finely ground basalt rock on farmlands extensively 2. Increasing the alkalinity of oceans by adding lime 3. Capturing carbon dioxide released by various industries and pumping it into abandoned subterranean mines in the form of carbonated waters How many of the above activities are often considered and discussed for carbon capture and sequestration?

All three activities are established Carbon Dioxide Removal (CDR) techniques: spreading basalt is "enhanced weathering," adding lime to oceans is "ocean alkalinity enhancement," and injecting carbonated water into subterranean formations is a proven method for "geological sequestration" (e.g., the CarbFix project). Option (b) is the most tempting wrong choice if one assumes sequestration is limited to gaseous CO2 storage, whereas carbonated water injection facilitates faster mineralization into solid rock. The core concept tested is the range of geoengineering and technological interventions used for Carbon Capture and Sequestration (CCS) to mitigate climate change.