单项选择题
Thethirdparagraphemphasizesinparttheimportanceof______.
单项选择题 WhenSusangotonthebus,thepassengers______.
单项选择题 “Thesameprinciple”(Para.2)referstotheprinciplethat______.
单项选择题 Theearliestpotatowasfoundin______.