Hi
Son los pantalones de Roberto. Son sus pantalones.
A- tus ==> your + plural noun <em>(not formal)</em>
B- mis ==> mines + pl. noun
C- sus ==> his + pl. noun <em>(his + your plural and formal)</em>
D- su ==> his + sing. noun <em>(his + your formal)</em>
+ singular noun + plural noun
yo mi mis
tú tu tus <em>(informal)</em>
él/ella/Us su sus
nosotros nuestro/ nuestra nuestros/nuestras
vosotros vuestro/vuestra vuestros/vuestras
ellos/ellas/Uds su sus
<em>They are Roberto's trousers. They are his trousers.</em>
The possessive adjective agrees in gender and number with the possessed noun, annd NOT with the possessor
Not 100% on this, but I thinks it's A.
