How long 主要是就一段时间提问。而含有一段时间状语的句子一般要用
现在完成时。在
一般现在时和一般过去时的句子中也会用到一段时间 。例如:I have been in this school for three years。如果就for three years提问,就要用How long 。抑或是I have been in this school since I came here three years ago(1998)。如果就since I came here three years ago提问,就要用when。因为I came here three years ago(1998)是一个时间点。