英语专业四级报名入口  状语从句
一、地点状语从句
    1. 地点状语从句通常由 where, wherever 等引导。例如：
    I found my key where I had left it.
    2. 有时某些地点状语从句含有条件关系。例如：
    Where there is a will, there is a way.
    二、条件状语从句
    1. 条件状语从句通常由 if, unless, in case, as / so long as, provided that, providing that, suppose that, supposing that, on condition that 等引导。例如：
    Would you give this letter to John if you happen to see him this evening?
    2. 条件状语从句中不能用将来时，其将来意义用现在时来表示。例如：
    If it is fine tomorrow, we'll go hunting.
    3. 注意 unless 与 if … not 的区别：虽然 unless 与 if … not 的意思一样，但 unless 只能用于真实条件句，而 if … not 除了可用于真实条件句之外，还可用于非真实条件句。例如：
    Unless you try, you will never succeed. = If you don't try, you will never succeed.
    If he were not present now, I would go away. （非真实条件句）
    三、原因状语从句
    1. 原因状语从句通常由 because, since, as, for, now that 等引导。