knock up against   (TTS發音)

meet by chance巧遇；偶然碰到

    I knocked up against my former teacher in the town this morning. 今天早上在城裡我遇見了我從前的那位老師。

    I didn't expect to knock up against so many difficulties when I started on this subject. 我沒有料到這項目一開始就遇上了這麼多的困難。