fall behind
phrasal verb with fall verb uk/fɔːl/ us/fɑːl/ fell | fallen
落在后面；落后
to fail to do something fast enough or on time
He was ill for six weeks and fell behind with his schoolwork. 他病了6个星期，落下了学校功课。
I've fallen behind on the mortgage payments. 我拖欠了按揭贷款。