1. Sister gave me a pen.

Question

2. My sister gave me a pen.

3. Brother handed me a dictionary.
4. My brother handed me a dictionary.
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Do we have to add 'My' before 'sister' and 'brother'? Or are they all grammatical?

Answer 1

Normal English includes "my" or "your" or some kind of modifier before "sister" or "brother" (or "mother" or .. ).

If you leave it out, it reads as if your sister's name is Sister and your brother's name is Brother.