(a) The pupils regretted their wrong-doings and promised never to make noise again. (b) They regretted their wrong-doings and promised never to be naughty again ( promised to never be naughty is probably more common, but not technically correct because of the split infinitive). (c) Remove "that" (d) Insert "to" between "never" and "be" (e) Remove "because of"; use "did"; replace "they" with "and" (f) They promised the headmaster.....
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