Final answer:
The vocabulary word that best fits into the sentence is 'treacherous'
Step-by-step explanation:
The vocabulary word that best fits into the sentence is treacherous. The adjective 'treacherous' describes something that is dangerous or risky. In the sentence, the speaker is afraid to cross the bridge because it appears unstable and unsafe, which aligns with the meaning of 'treacherous'.
Learn more about the meaning of the word 'treacherous'