Respuesta :
Answer: B) Since
Explanation:
Whenever the word 'Since' Is used in a sentence, it is used to refer to a cause and effect statemet. Sort of like when someone uses the word because, the first thing that comes to mind is cause and effect. Ex; "ohh, the window broke because a ball was thrown into it."
Since served as a clue that there is a cause and effect. Since indicates that one thing (the desert air) caused another thing to happen (the bread turning stale).