Why Is It Best to Use Specialized Software to Estimate $\tau$

Multiple Choice

Why is it best to use specialized software to estimate 2SLS?

A) specialized t-values are needed for inference and hypothesis testing
B) the $\tau$ distribution is not widely available otherwise
C) it is algebraically difficult to find structural parameter estimates from reduced form estimates,so the software needs to use specialized algorithms when algebra does not work
D) it is too easy to make a data handling mistake when capturing predicted values to use as regressors in the second stage