Calculate.

a) [[$ \dfrac{b^2 \cdot b^4}{b^3} = $]]

b) [[$ \dfrac{c \cdot c^3 \cdot c^5}{c \cdot c^2} = $]]

c) [[$ \dfrac{c^3d^4}{c^3d^3} = $]]

d) [[$ \dfrac{y}{x^2} = $]]