Learn Romanian: Fetele fug în parcul vechi. - The girls run in the old park.

The verb here is a fugi (to run), which belongs to the fourth conjugation group ending in -i. For many regular verbs in this group, the they form (ei / ele) is identical to the I form (eu). The -i ending is dropped, leaving just the root fug. You know it means they run because the subject is fetele (the girls).

Normally we say în parc for in the park. Why does parc have the definite article -ul attached here?

Excellent catch! You learned earlier that prepositions like în usually hide the definite article, so in the park is just în parc. However, Romanian has a special rule: if the noun is followed by an adjective like vechi (old), the definite article comes back. That is why it becomes în parcul vechi.

Does the adjective vechi end in -i because the sentence is plural?

No, in this sentence it is actually singular! The word vechi (old) is a bit unusual because its base singular form for masculine and neuter nouns already ends in -i. Since parc is a neuter noun in the singular, vechi is also in its singular form to match it.

How do we build the word fetele from the basic dictionary word for girl?