on earth这一词组在句中为的是加强语气，其意为"究竟"、"到底"。而作为"地球"讲时则要加定冠词，如：How far is the earth from the moon. 而作为"泥土"讲时则为不可数名词，如：He filled the pot with earth and wanted to plant some flowers.
［误］ What on the earth do you mean?
［正］ What on earth do you mean?
［析］ on earth这一词组在句中为的是加强语气，其意为"究竟"、"到底"。而作为"地球"讲时则要加定冠词，如：How far is the earth from the moon. 而作为"泥土"讲时则为不可数名词，如：He filled the pot with earth and wanted to plant some flowers.
