A) They shake our hand - ellos sacuden nuestra mano B) They shake each other's hand - <span>se dan la mano C) You shake their hand - </span>agitas su mano D) We shake each other's hand - <span>Nos damos la mano a los demás
B) they shake each other's hand The verb in this sentence,"se dan", comes from "darse", which is a reciprocal verb (verbo recíproco) and these verbs always talk about something that the speakers are mutually doing, so the other options wouldn't be correct because: 1) They aren't referring to the 3rd person of plural, 2) They aren't doing a reciprocated action. Hope this helped you :)
