∵z=
1+2i
1+i =
(1+2i)(1-i)
(1+i)(1-i) =
3+i
2 =
3
2 +
1
2 i ,
∴
.
z =
2 -
2 i .
∴z的共轭复数的虚部是-
2 .
故选:C.