Continue the Sequences

  1. brain, cable, decline, end, free, gift, higher
    (first and third letters in alphabetical sequence)
  2. abacus, elder, specific, brook, humour
    (successive vowels occur twice)
  3. trail, rabbit, patter, stop, cats, automatic, tea
    (first letter of each word is last letter of next)
  4. cobra, neutron, dentist, concerts, plinths, strenghts
    (position of last vowel from end of word)