Answer:
The correct answer is el.
Introduction to Subjects in Spanish
From the subjects you have provided, these indicate masculinity or femininity as well as singularity or plurality.
Of these articles, there are two singular articles: el and la.
There are also two plural articles: los and las.
In terms of masculinity and femininity for the articles:
There are two masculine articles: el (singular) and los (plural).
There are also two feminine articles: la (singular) and las (plural).
Solution
Refer to the noun that you are given: cuaderno.
This noun is masculine and singular for two reasons:
- The noun ends in an -o (which typically indicates masculinity), whereas when a noun ends in an -a, it typically indicates femininity.
- The noun does not end in -os (which typically indicates plurality), whereas when a noun ends in an -as, it typically indicates femininity.
Therefore, since it is both masculine and singular, this indicates that the applicable article will be el.