Ответ:

  1. a) They spoke English in India since the English went there in the 18th century.
  2. b) Some Russians heard only French in the 18th and 19th centuries.
  3. a) The number of English speakers rose steeply in the last 50 years.
  4. b) I had just bought a house when house prices rose dramatically.
  5. a) Jack's English