at,for,since的选择填空题
这道题目不确定选那个词,麻烦高手帮解答和说明为什么选这个答案.谢谢
IntheUK,inbusinesssituations,whenyoumeetsomeone_____thefirsttimeyoushakeyourhandsandsay,"howdoyoudo?".
A.atB.forC.since