Let f=f(y;x),y>0 be a probability mass function that depends on the unknown parameter x, has continuous first and second order derivatives, and the support of f does not depend on the x.

1.show that the constant estimator x'=x, where x is the true value, is a minumum variance unbiased estimator for x.

2.what is the variance of x'?

3.and why the Cramer-Rao lower bound for f is not necessarily lower bound for x'=x?