Which sentence shows the correct use of personal pronouns?
"This is Silvia. She is my best friend. Next week, we will go to school together."
"This is Silvia. Her is my best friend. Next week, we will go to school together."
"This is Silvia. She is my best friend. Next week, us will go to school together."
"This is Silvia. She is my best friend. Next week, they will go to school together."