The "Miyawaki method" is well known for the:

1. A

   Promotion of commercial farming in arid and semi-arid areas

   Commercial farming in drylands. Not Miyawaki.

2. B

   Development of gardens using genetically modified flora

   GM gardens. Not Miyawaki.

3. C

   Creation of mini forests in urban areas

   Mini forests in urban areas. Dense, fast, native planting on small plots.

4. D

   Harvesting wind energy on coastal areas and on sea surfaces.

   Wind harvest. Unrelated.

Summary. Official key is (c). The Miyawaki method packs native seedlings densely to grow a multi-layer mini-forest quickly — used on urban scraps of land.