Assuming each customer can be uniquely identified either by using the Customer ID or by the mobile phone number, which of the following statement is false?

Select one:

a. Both customer id and mobile phone number should be combined to make it a primary key

b. Customer ID can be a primary key.

c. Mobile phone number can be a primary key

d. If mobile phone number is a primary key, it is good to include the prefix 61 representing the country code before a mobile number such as 0499 789 629 to make it truly unique across the world