50．應工程師的書面要求，承包人應根據工程師的指令，對施工過程或維修期內出現的任何欠缺、不足或缺陷進行檢查。除非根據契約，此種欠缺、不足或缺陷應由承包人負責，否則上述檢查工作的費用由業主承擔。如此種欠缺、不足或缺陷如上所述屬於承包人的責任，上述檢查費用應由承包人負擔，且他應按本契約第49條的規定，自費對其進行修理、修正和補救。
alterations，additions and omissions
變更、增加和省略
51．（1）the engineer shall make any variation of the form，quality or quantity of the works or any part thereof that may，in his opinion，be necessary and for that purpose，or if for any other reason it shall，in his opinion be desirable，he shall have power to order the contractor to do and the contractor shall do any of the following：
51．1如工程師認為必要，他應對整個工程或任何部分的形式、質量或工作量作相應變更，且他有權因其他任何理由，命令承包人作出且承包人必須作出以下變更：
（a） increase or decrease the quantity of any work included in the contract，
增減契約所規定的工程量，
（b）omit any such work，
省略任何部分工程，
（c) change the character or quality or kind of any such work，
改變任何部分工程的特性或質量或類別，
（d）change the levels，lines，position and dimensions of any part of the works，and
改變任何部分工程的平面、型線、位置和面積，
（e）execute additional work of any kind necessary for the completion of the works
增加竣工所需的任何額外工程，
and no such variation shall in any way vitiate or invalidate the contract，but the value，if any，of all such variations shall be taken into account in ascertaining the amount of the contract price．
但此種變更不得以任何方式使契約失效，此種變更所需的一切費用（如果有）應在確定契約價格時予以考慮。
（2）no such variations shall be made by the contractor without an order in writing of the engineer．provided that no order in writing shall be required for increase or decrease in the quantity of any work where such increase or decrease is not the result of an order given under this clause，but is the result of the quantities exceeding or being less than those stated in the bill of quantities．provided also that if for any reason the engineer shall consider it desirable to give any such order verbally，the contractor shall comply with such order and any confirmation in writing of such verbal order given by the engineer，whether before or after the carrying out of the order， shall be deemed to be an order in writing within the meaning of this clause．provided further that if the contractor shall within _______ days confirm in writing to the engineer and such confirmation shall not be contradicted in writing within _______ days by the engineer，it shall be deemed to be an order in writing by the engineer．