Include is the third-person singular present tense of includere.
Here the subject is L'arco narrativo, which is singular, so the verb must also be singular:
So L'arco narrativo include... means The narrative arc includes...
Not exactly. It is an Italian word, even though it looks very similar to the English one.
A rough pronunciation is:
een-KLOO-deh
More precisely, the stress falls on the u sound: in-CLU-de.
Also, the final e is pronounced in Italian, unlike in English.
Because sottotrama is a feminine singular noun, so it takes the feminine singular indefinite article una.
If the noun were masculine, you would use un or uno instead, depending on the word.
It is a compound noun:
So sottotrama literally means something like sub-plot, which matches the English word subplot very closely.
It is written as one word in Italian.
Italian often uses the definite article where English also uses the, but it can also use it in some places where English would not.
In this sentence, L'arco narrativo refers to the narrative arc as a defined concept or element, so the definite article is completely natural.
Similarly, una sottotrama means a subplot, meaning one subplot, not a specific already-known one.
Yes, often you could.
Both can work in many contexts.
Include is very close to English and sounds natural here.
Comprende can sometimes sound slightly more formal or more like comprises, depending on context.
So L'arco narrativo comprende una sottotrama is also possible.
The normal, neutral Italian word order here is:
subject + verb + object
So:
L'arco narrativo include una sottotrama.
Italian word order can change for emphasis, but this standard order is the most natural and the best one for a learner to use first.
Una sottotrama means a subplot, so it introduces one subplot, not a specific previously identified one.
If you said la sottotrama, that would mean the subplot, referring to a specific subplot already known from context.
So the choice between una and la matters: