2. If the complex number $z=a+b \mathrm{i}(a, b \in \mathbf{R}),|z-\mathrm{i}|>|z+\mathrm{i}|$, then $(\quad)$.
A. $a>0$
B. $a0$
D. $b<0$
2. D. From $|a+(b-1) \mathrm{i}|>|a+(b+1) \mathrm{i}|$ we know $a^{2}+(b-1)^{2}>a^{2}+(b+1)^{2}$,
$\therefore \quad 4 b>0, \therefore \quad b<0$, hence choose D.