

Because we feel tired at bed time, it is natural to assume that we sleep because we are tired. The point seems so obvious that (01) _______ anyone has ever sought to question (02) _______ nevertheless, we must ask “tired (03) _______ what?” People certainly feel tired at the end of a hard day’s manual work, but it is also unquestionable that office workers feel equally tired when bedtime (04) _______ Even invalids, confined (05) _______ beds or Wheelchair, become tired (06) _______ the evening wears on. Moreover, the manual worker (07) _______ still feel tired even (08) _______ an evening spent relaxing in front of the television or (09) _______ ; a book, activities which ought to have a refreshing effect. There is no proven connection between physical exertion (10) _______ ; the need for sleep.