It is a really good book for you study English. In this book you can study how to speak English and many grammatical points of English language which are very important. This book is more than 40 mb, so it may take you a little long time to download. And the book is also designed for self-study. You can learn by yourself without any teachers to guide you because the book will be a teacher for you.
English 900 is a very famous English book in our country. You may have already read this book since you were a child. You can get or buy this book almost anywhere, from small local book shop to big book centers such a Sarpayloka or Sarpay Bimhan. The price of this book will not be too high because this is a book which was published many decades ago, so the price will be relatively cheap since it is a old book.