the operation,which lasted for over four hours,proved to be verydifficult because of the hard resin which covered the skin.最后一个,为什么加which,用定语从句hard resin已经是主语了,再加一个which不是多余吗请问可不可以

French doctors and American scientists have reported doing an operation in which the doctor was out the requested clipboard operation the sameness in operation the operation has timed The operation has 英语翻译Since the first acid-gas injection operation in 1990,51different injection sites have been approved,of which 44 arecurrently active.One operation was not implemented,three wererescinded after a period of operation (either because injectio by implementing which the level of daily operation and management of the Department of Engineering没看懂. After the operation什么意思 The operation has timed-out. 英语翻译But perhaps the most damning indictment of the entire operation is the actual accusation made against the illegals:after a surveillance operation spanning at least a decade,during which they were tailed and their conversations bugged,thei 英语翻译now operation smile helps chidren in more than twenty developing countries and has cured about ten thousand children.Operation smile has won many prices for its work and in1999,another special activity was started,which was called the wo 英语翻译now operation smile helps chidren in more than twenty developing countries and has cured about ten thousand children.Operation smile has won many prices for its work and in1999,another special activity was started,which was called the wo 英语翻译Computer software can be roughly divided into two kinds:the system programs,which manage the operation of the computer itself,and the application programs,which solve problems for their users.The most fundamental of all the system program The doctor p_______ the operation successfully. The doctor performed the operation with succes. 英语翻译(30)This report is a preliminary assessment of the mining potential of the Mokau Coalfield which has been carried out along with an assessment of the environment factors which might affect mine development and operation.The report include 英语翻译The smooth operation of an ant conlony depends on ten to twenty different signals,most of which are pheromones(chemical signals triggering behavioural responses). the operation,which lasted for over four hours,proved to be very difficult.请问prove to be是词组还是什么,不加to be行不行