Question 17:
B. c-a-b

Question 18:
A. I will definitely attend the festival again next year.

Question 19:
A. on

Question 20:
A. these

Question 21:
C. However

Question 22:
A. which

Question 23:
D. Although

Question 24:
C. playing

Question 25:
D. The more the economy grows, the better people's living condition is.

Question 26:
A. Unless you try to work hard, you will fail the final exam.