Do I have to use the subject in every sentence?
No, actually if you do it you will sound strange, although it is grammatically perfect. However, since verbs have different ending for each person, the pronoun can be omitted.
PA
Related Spanish GCSE answers
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(From a comprehension piece) what is the percentage of English trade that is with countries that do not speak English?
How do I form the future tense of a verb?
Conjugate hablar in the imperfect tense.