46. During the cell cycle, in which phase does DNA replication occur? (A) G1 phase (B) S phase (C) G2 phase (D) M phase

48. Nitrogen gas (N₂) in the soil cannot be directly used by plants and must undergo nitrogen fixation. In nature, the process of converting N₂ to ammonia (NH₃) primarily relies on the participation of which of the following organisms? (A) Mycorrhizal fungi (B) Nitrogen-fixing bacteria and cyanobacteria (C) Algae in lichens (D) Digestive enzymes of carnivorous plants