空谷传声kōnggǔ-chuánshēng熟be prompt in response

空谷幽兰kōnggǔ-yōulán熟lonely orchid in a deserted valley—of a personbe noble in character

空谷足音kōnggǔ-zúyīn熟the sound of footsteps in a deserted valley—difficult-to-come-by information, opinion, thing, etc；sth rare and precious