However, seek this resource . Support the publishers by buying a legitimate e-copy from S. Chand or an authorized retailer. The cost is minimal compared to the lifetime of English proficiency you will gain.
Finally, remember that a key is useless if you never build the door. Use the Key not as a shortcut, but as a tool for verification. Attempt every exercise twice—once blind, and once with correction. Do this, and you will not only pass your middle school exams but will build a command of English grammar that will serve you in high school, college, and your career.
Write your answers in a separate notebook. Do not write in the textbook.