For each of the following functions classify the isolated singularity at 0 and specify the principal part of the Laurent development there:
a) $\dfrac{sin(z)}{z^n},\;n\in\mathbb{N}$
b) $\dfrac{z}{(z+1)sin(z^n)},\;n\in\mathbb{N}$
c) $cos(z^{-1})sin(z^{-1})$
d) $(1-z^{-n})^{-k},\;n,k\in\mathbb{N}\setminus\{0\}$
I think that in a) $0$ is a removable singularity, in b,c and d $0$ is an essential singularity, but what does it say specify the principle part of the Laurent development? How do I do it?