Final answer:
During online or mobile app registration for a hotel or service, guests are commonly required to provide credit card information and a valid email address.
Step-by-step explanation:
When a guest registers online or with a mobile app, they are typically not required to provide their Social Security number (d). Instead, common requirements include providing a credit card information (c) to reserve and guarantee the booking or service, and a valid email address (d) for confirmation and communication purposes. Photo identification (b) may be required upon physical check-in at a hotel, but not necessarily during the online/mobile registration process.