Final answer:
Sidewalk ramps and Braille signs are considered both accommodations required by the ADA and forms of accessibility for people with disabilities, hence the correct answer is 'both b and c'.
Step-by-step explanation:
Sidewalk ramps and Braille signs are critical elements that contribute to the accessibility for people with disabilities. These features are not only examples of accommodations required by the Americans with Disabilities Act (ADA) but are also forms of accessibility in a broader sense that enable individuals with disabilities to navigate and interact with their environment more effectively. To answer the student's question, the correct option would be d. both b and c because these elements serve both as mandated accommodations under the ADA and as practical means to achieve greater accessibility.