29 c however
30 b therefore
31 a nevertheless
32 a should
33 it's a rule so everyone has to stricly follow (đề sai) chon d
34 d because
35 c while
36 d so
37 b but
38 c moreover
39 lac long quan miss his life in the sea therefore he took 50 sons back there( đề sai) chọn a
40 b was watching
good luck