Вставьте as...as, so...as. 1)This book about the UK is __ heavy

1) This book about the UK is as heavy as that one. 2) These mountains are as old as those mountains in the USA. 3) Now he speaks English not so fluently as he did a year before. 4) The Volga is not so long as the Nile. 5) Literature is as interesting to me as History.

Вместо not so...as можно использовать и not as...as. Сообразно "English Grammar Today" (Cambridge), вариант not so...as менее всераспространен.