81. The children themselves are not in any way to blame for the disaster. ("In no way" is a common phrase meaning "not at all")
82. The existence of extraterrestrial life is not confirmed by the report. ("Under" wouldn't be appropriate here. The report simply doesn't confirm or deny)
83. I was never shown how to operate the machinery. ("At" wouldn't be suitable in this context)
84. He never suspected that she was a witch. ("At" doesn't work here)
85. There has never been a time when the English language was not in a state of change. ("At" wouldn't be the best choice)
86. You shouldn't send money to us by post under any circumstances. ("Under" works well here to indicate any situation)
87. We can't change the ticket in any circumstance. ("In" is appropriate for any situation)
89. He booked tickets for the afternoon performance and the evening performance as well. ("As well" connects the two performances)
90. The burglars stole a thousand pound's worth of electrical goods, and left the flat in an awful mess. ("And" connects the two actions)
91. Tom was not only late, but he had left all his books behind. ("Not only" introduces the first issue, followed by "but" and the second issue)