Analyzing possessive expressions

More analyzing on possessive expressions ...whether I like it or not :) New words I am learning today are:

1. هُنَاكَ there.
2. مَنْ only today I learned that مَنْ not only means who but also whose.
3. تَحْتَ under.
4. هُوَ other than he, هُوَ also means it.

Rules of possessive expressions learned from previous lessons should be analyzed carefully in the following sentences:

1. سَعِيْدٌ: أَكِتَابُ مُحَمَّدٍ هَذَا؟ Saeed: Is this Muhammad's book?
   .يَاسِرٌ: ﻻَ, هَذَا كِتَابُ حَامِدٍ Yasir: No, this is Hamid's book.
2. سَعِيْدٌ: أَيْنَ كِتَابُ مُحَمَّدٍ؟ Saeed: Where is Muhammad's book?
   .يَاسِرٌ: هُوَ عَلَى الْمَكْتَبِ هُنَاكَ Yasir: It is there on the desk.
3. سَعِيْدٌ: أَيْنَ دَفْتَرُ عَمَّارٍ؟ Saeed: Where is Ammar's notebook?
   .يَاسِرٌ: هُوَ عَلَى مَكْتَبِ الْمُدَرِّسِ Yasir: It is on Teacher's desk.
4. سَعِيدْ:ٌ قَلَمُ مَنْ هَذَا؟ Saeed: Whose pen is this?
   .عَلِيٌ: هَذَا قَلَمُ الْمُدَرِّسِ Ali: This is the teacher's pen.
5. سَعِيْدٌ: أَيْنَ حَقِيْبَةُ الْمُدَرِّسِ؟ Saeed: Where is the teacher's bag?
   .عَلِيٌ: هِيَ تَحْتَ الْمَكْتَبِ Ali: It is under the desk.