crop out

(of rock) appear or be exposed at the surface of the earth

（巖石、石頭）露出地面；露頭

crop up

To appear unexpectedly or occasionally

意外出現(xiàn)，偶然出現(xiàn)

“one of the many theories that keep cropping up in his story”(&b{Christopher Lehmann-Haupt})

“一個在他的故事中不斷意外出現(xiàn)的理論”(&b{克里斯托夫·萊曼——豪普特})