Answer:
The right option that fills the blank is:
- Since “la semana” is femenine, when you say “the first week” the word primera is written in the feminine form.
Explanation:
A simple way to determine if a noun is masculine or feminine is to identify that feature in the given article that accompanies it (if it has one) since each of these four articles applies to a specific gender and number as sample below:
- La: Female and singular.
- El: Male and singular.
- Las: Female and plural.
- Los: Male and plural.
Since the mentioned noun is "la semana", it can be recognized that the noun is feminine and plural, taking this into account it must be recognized that the adjectives must also bear these traits, that is, in this case, the adjective "primero", must be in its feminine and singular form:
- Primero: Male and singular.
- Primera: Female and singular.
- Primeros: Male and plural.
- Primeras: Female and plural.
The reason why is selected the form "primera".
