Which word correctly identifies the subject of the sentence?

For example, the sentence "Er öffnet das Buch und beginnt die komplizierten Texte zu lesen."

In this context, 'Er' is a personal pronoun used in the nominative case, indicating the subject of the sentence, translated as 'He' in English. The pronoun 'Er' is essential here as it refers to a specific male subject who is performing the action. All the other options are personal pronouns as well but in different forms such as 'Ihr' (You - formal), 'Du' (You - informal) and 'Es' (It), and would not fit in this sentence gramatically.