The word "la maestra" is feminine because it is preceded by the feminine article "la". In Spanish, nouns are assigned a gender, either masculine or feminine, and this determines the article that accompanies them. In this case, "maestra" is a feminine noun, referring to a female teacher. The other options, "el cuaderno", "el abuelo", and "el banco", are all masculine nouns, as they are preceded by the masculine article "el".