This sentence stands for the imperative mood. This mood is used when telling someone to do something. In other words, these are <em>commands. </em>So almuerce is the formal command that comes from the verb almorzar (to have lunch). Therefore, we can write and translate this sentence as follows:
<em>Señora, </em><em>almuerce </em><em>en el parque (Lady, have lunch in the park)</em>
These rogue nouns have something in common: they are all feminine, singular and they all start with an accented “a” sound (a-, ha-). The agreement rule specifically says that if a noun is feminine and singular, the indefinite article you have to use is una.
