‘X’ contracts with ‘Y’ to purchase 30 chairs of a particular brand called make and type. ‘Y’ delivers 15 chairs of that quality and 15 chairs of some other make - 於4shared.com下載。 ‘X’ contracts with ‘Y’ to purchase 30 chairs of a particular brand called make and type. ‘Y’ delivers 15 chairs of that quality and 15 chairs of some other make 提供免費檔案分享的4shared網站儲存資料。