Use the "Passive Voice" to describe the incident (e.g., "The piano was dropped by the pilot").
If you are referring to , Lesson 21 is titled "Which book?" . This much simpler lesson focuses on basic object identification and the use of the word "one" as a pronoun (e.g., "Give me a book, please... Which book? This one?"). " or perhaps exercises related to its grammar? New Concept English 2 | PDF - Scribd New Concept English Practice And Progress Audio 21