Solution (source code)

= Solution
{c}

Apply part (a) to the entire function $f(z)=e^{i\theta}z$. Its derivative has modulus one, so its <conformal Brownian clock> is $A_t=t$. Thus
$$
e^{i\theta}Z_t=e^{i\theta}Z_0+\widetilde Z_t,
$$
which is a <planar Brownian motion> starting from the rotated initial point. In particular, if the initial point is zero, its law is unchanged. This is <rotational invariance of planar Brownian motion>.