The Americans celebrate Thanksgiving Day to show their gratitude to ______.

A．Americans show respect to their forefathers.
B．The Pilgrims raised turkeys.
C．The Pilgrims did not know what to grow after they got to Plymouth.
D．Today a lot of guests are invited to celebrate Thanksgiving Day.

A．a geography book
B．a book about customs
C．a travel book
D．a book about the American way of life