A
关于but的用法：当有实意动词do时,后面的动词不加to；没有do的,要加to.即“有do不带to；没有do要带to”
举例：Hearing this news,she did nothing but cry.
Hearing this news,she didn`t say anything but to cry.
第二句话里面的didn`t,是助动词哦,跟第一句不一样的,特意举这样的例子给你,注意区分.