a) NaOH is a strong nucleophile and strong base. The substrate in this case is primary. Therefore, we expect S_N2 (giving the major product) and E2 (giving the minor product).

b) NaSH is a strong nucleophile and weak base. The substrate in this case is primary. Therefore, we expect only S_N2.

c) When a primary alkyl halide is treated with t-BuOK, the predominant pathway is expected to be E2.

d) DBN is a weak nucleophile and a strong base. Therefore, we expect only E2.

e) NaOMe is a strong nucleophile and strong base. The substrate in this case is primary. Therefore, we expect S_N2 (giving the major product) and E2 (giving the minor product).