Option 1 -> Includes (A) which is incorrect as wild tea plants were discovered in Assam, not a shortage.
Option 2 -> Includes (A) and (C); (A) is incorrect and (C) refers to labor demand that arose later with expansion.
Option 3 -> Includes (C) which addresses labor issues during expansion, not initial cultivation challenges.
Option 4 -> Correctly identifies (B) and (D) as the passage explicitly states "the initial years were challenging due to lack of knowledge about tea cultivation techniques and the hostile climate and terrain of Assam."
Hence, Option 4: (B) and (D) only -> The passage clearly mentions the two initial challenges: ignorance about cultivation techniques and the hostile climate/terrain, while wild tea plants were already discovered (eliminating A) and labor shortage became an issue only during later expansion phases (eliminating C) -> correct