Rules 9 and 10
9. Possessive Apostrophe Error
The dog`s trainer is training the dog intensely. (Correct).
You have to add an apostrophe and an "s" to show a noun`s possession of another noun.
10. Verb Tense Shift
Last weekend, I walked to my friend`s house and rode his bike home
When you write a sentence, be sure to make all the verbs in the same tense.