Ever since the world began nations have difficulty in keeping peace with their neighbors.()

单项选择题The old artist is in the habit of going for a walk in the park every morning except it rains.()

A. in the habit of
B. going for
C. morning
D. except it rains

单项选择题Nancy had a great deal of trouble to concentrate on her work because of the noise in the next room.()

A. a great deal of
B. to concentrate on
C. because of
D. in