对于一个小国(价格接受国)来说,最优关税为()。
A、零
B、禁止关税
C、毫无疑问的是正值
D、随着国家需求弹性的增加而增加
用I doubt whether/if/I don't doubt that There is no doubt that/about/without doubt 完成句子。
There is no doubt _____ our experiment will succeed.
There is some doubt _____ she will come on time.