Write the complex number $4$ in polar form.

a$)4(cos0isin0)$

b$)4(cos(\frac{5}{3})isin(\frac{5}{3}))$

c$)2(cos(\frac{5}{4})isin(\frac{5}{4}))$

d$)4(cos(\frac{7}{6})isin(\frac{7}{6}))$