All items except (a) are workable with the Masther theorem. In case (a), the toll function is not a polynomial and, thus, the Master theorem does not apply. But one can solve it by expansion:
T(n) = 2^n + T(n/2)
= 2^n + 2^(n/2) + T(n/4)
= 2^n + 2^(n/2) + 2^(n/4) + T(n/8)
= ...
= O(2^n).
The result is clear by intepreting the recurrence as sums of binary numbers: 1+10+100+10000+10000000 <= 2*10000000.