a) All phone numbers must include the area code
b) Certain fields are required (such as the email address, or phone number) before the record is accepted
c) Information on the customer must be known before anything can be sold to that customer
d) Then entering an order quantity, the user must input a number and not some text (i.e., 12 rather than ‘a dozen’)

Answer: c
Explanation: Information on the customer must be known before anything can be sold to that customer