fall behind

Từ điển tiếng Anh - Cambridge Advanced Learners Dictionary

fall behind phrasal verb [ fell behind fallen behind fallen behind falls behind falling behind ]
to fail to do something fast enough or on time
• He was ill for six weeks and fell behind with his schoolwork.
• I've fallen behind with the mortgage payments.
Thesaurus⁺: ↑Failing and doing badly
Main entry: fall_{phrasal verb}