答案：D

题目分析：句意：我太累了以至于我不能跑了。让我们停下来放松一下。so...that...如此...以至于...that后面跟从句too...to... 太...而不...；adj.得...to后面直接跟动词This was so cheap that I had to buy it.这个太便宜了，以至于我非买不可。This was too cheap to pass.这个太便宜了，不买不行。故选D