According to the meaning of the question: the middle five days are uncertain, but the head and tail are required to be three, indicating that there is no more or less in the middle, and the middle refers to the six intervals in the middle of these seven days:

(1) If all six intervals are flat, 1 species.

② 1 upper 1 lower 4 grades: A26=30 species.

③2 Up, 2 Down and 2 Flat: C26 C24=90 kinds.

④3 Up and down: C36=20 species.

*** 14 1, the previous answer is a bit wrong. . It should be all right now.