The Urim and Thummim were objects used by the priests of ancient Israel to discern God's will. How were they typically understood to function according to biblical accounts?

A They were carried in the priest's breastplate and used for casting lots to receive God's guidance. B They operated as a pair of stones that emitted light to indicate divine approval or disapproval. C They were a set of sacred writings kept in the Ark of the Covenant that provided direct answers. D They were a collection of sacred symbols interpreted exclusively by the High Priest.