_________ receipt of your enquiry, we shall airmail you immediat

_________ receipt of your enquiry, we shall airmail you immediately our quotation sheet.
【正确答案】：Upon/On
【题目解析】：【考点点击】本题在2009年4月真题第二大题39小题考查过，主要考查receipt的搭配。【要点透析】upon/on receipt of表示“一收到就”; in receipt of sth.表示“已收到 ”。