Final answer:
The signal word that helps readers understand what caused Teresa's father to have a difficult time finding work is 'because'
Step-by-step explanation:
The signal word that helps readers understand what caused Teresa's father to have a difficult time finding work is because.
For example, if the sentence says, 'Teresa's father couldn't find a job because the economy was in a recession,' the word 'because' indicates that the reason for his difficulty finding work is the state of the economy.