Consider the Enhanced Entity-Relationship Diagram in Table 2 on the next page and answer the following questions by ONE sentence each. Note that attribute total refers to the total billing amount of an order.

(a) Explain whether there can be an order that is neither a phone order nor a table order.

(b) Which attribute, or set of attributes, uniquely identifies a table?

(c) Explain whether it is possible to compute the total billing amount of all (phone and table) orders placed in one specific restaurant.

Receives_by_phone Restaurant hone_line phone num Contains dateTi me billingNo total Order Originates from Table optional.orh number PhoneOrder TableOrder street wai ter deliveryAddress postcode city