21.   This system has worked well for some of our most successful business enterprises, particularly in the technological and medical industries.

22.   This system works to the disadvantage of women.

23.   Would you just explain to us how the system works.

24.   He explained how the system worked.

25.   We shall find out which system works most effectively.

26.   The system worked perfectly.

27.   We need to assess whether or not the system is working.

28.   The book can be read with profit by anyone who wants to understand how the system works.

29.   There is a great deal of confusion about how the system works.