46. ____ I was very much mistaken, there was something wrong with Louise.

　　A) Unless

　　B) As

　　C) Though

　　D) Since

　　47. He is not under arrest, _____ any restriction on him.

　　A) or the police have placed

　　B) or have the police placed

　　C) nor the police have placed

　　D) nor have the police placed

　　48. We could _____ him with a detached house when he came, but he had specially asked for a small flat.

　　A) provide

　　B) have provided

　　C) not provide

　　D) not have provided

　　49. This missile is designed so that once _______ nothing can be done to retrieve it.

　　A) fired

　　B) being fired

　　C) they fired

　　D) having fired

　　50. ______ the two, Bob is _____ student.

　　A) Of, more diligent

　　B) In, more diligent

　　C) Of, the more diligent

　　D) In, the more diligent

　　51. _______, he would not have recovered so quickly.

　　A) Hadn't he taken good care of

　　B) Had he not been taken good care of

　　C) Had not he been taken good care of

　　D) Had he bee not taken good care of