Final answer:
U-turns are typically illegal in situations where they present significant dangers to traffic, such as on highways, at the top crest of a hill or curve, and at railroad crossings. The correct option that includes all the places where making U-turns is not legal is 'd. all of the above'.
Step-by-step explanation:
The question pertains to the legality of making U-turns in specific situations. It's important to understand traffic laws to maintain safety on the roads. When considering the legality of U-turns, laws often vary by location, but there are common situations where making U-turns is generally prohibited.
They include making U-turns on highways due to the high speeds and heavy traffic conditions, making U-turns at the top crest of a hill or curve where visibility is limited and other drivers may not be able to see your vehicle in time to avoid a collision, and at railroad crossings where stopping or turning could be highly dangerous due to the potential for an oncoming train.
Each of these situations presents unique hazards, and the rules are put in place to prevent accidents. Therefore, the correct option in this case is d. all of the above.