labour at(或over)

• 致力于…，辛苦地干；在…上绞尽脑汁：

  The teacher asked his students to labour at obligatory courses.

  老师要求学生在必修课上多下工夫。

  There's no point in labouring at a tedious task.

  辛苦地干单调乏味的工作没有意义。

  The president laboured over his speech before he had it in final form.

  总统在演说稿定稿之前进行了辛苦的修改。