1。 Backpack (backpack with context-aware lost items)

2。 On (ground fixed collocation)

3。 This (pronoun usage)

4。 This is not my backpack (negative sentence)

5。 Yours (adjective possessive pronoun)

6。 My (adjective possessive pronoun)

7。 This (pronoun usage)

8。 Thank you (expressing gratitude)

9。 Welcome (you're welcome)