latchkey child
(becoming dated 渐旧) child who has to let himself into his house or flat and look after himself, esp after returning from school, because both parents are out at work 挂钥匙的儿童(尤指因父母外出工作, 故放学回家需自行进屋的).
After switching on powerful arc lights, they saw great stalagmites -- some of them over forty feet high -- rising up like tree-trunks to meet the stalactites suspended from the roof.