15Which of the following statements is TRUE of restaurants in Britain?
选项：

A:

Most of them serve British food.

B:

A tip about 10% of the bill for the waiter is usually considered inadequate.

C:

If you reserve a table, you don't have to include a tip for the waiter.

D:

If a service charge is included in the total on the bill you don't have to tip the waiter.