In Ideal Circumstances, the Optimal Way to Track Individual Behaviour

In ideal circumstances, the optimal way to track individual behaviour at a website thereby allowing a true picture of website usage and estimating return on investment is to:

A) use clickstream analysis.
B) use a combination of web- centric and audience- centric measures.
C) use page impressions combined with time spent online measures.
D) use log files.
E) allow only subscribers access to a site.