27) C1 ∩ C2 = (C1' ∪ C2')'

Note: C1' denotes complement of C1.

Now, C1' is a tribe and C2' is also a tribe. And union is two tribes is a tribe therefore, (C1' ∪ C2') is a tribe. Hence, complement of (C1' ∪ C2') = (C1' ∪ C2')' will be a club.Hence, option(a)

28) C1 ∪ C2 = (C1' ∩ C2')'

Now, C1' and C2' are tribes. So, their intersection will also be a tribe. And therefore, the complement of

(C1' ∩ C2') = (C1 ∩ C2)' will be a club. Hence, option(c)

29) Society and Empty set are both Club and Tribe.Hence, option(b)

30)Given a tribe T1 and a club C2: (T1 ∩ C2') is a club since C2' is a tribe and the intersection of two tribes is a tribe. Hence, option(b)

:)