学生疑问：

1. I was down with the flu a couple of months ago and I cured myself.

2. I’ve had headaches off and on for the last few years, but none was as bad as this.

老师答疑：a couple of months ago →从现在算起“两个月之前”的那个时间点（当时我得了流感，现在好了）。强调的是过去的一个事件，所以用一般过去时。for the last few years →从几年前到现在持续的一段时间（断断续续头痛）。强调持续到现在的状态，所以用现在完成时（have had）。

分析点评：ago = 站在“现在”回头看，指着过去的某个点。for =画一条线，从过去的某个点一直连到现在（或某个终点）。