D. Connaissent. Because the ending -ent is the conjugation of the pronoun yours. The subject of the sentence refers to multiple people.
To an adult : bonjour
to a friend : salut .
Bonjour !!
Elle rentre d'Italie.
elle + rentre <em>(3e pers. singulier)</em>
<em />
d' + Italie <em>(de + vowel => d')</em>
<em />
<em>☺☺☺</em>
