A. The left lane unless overtaking.
A. The left lane unless overtaking.
B. The right lane to avoid slow moving vehicles.
C. Either left or right lane.
Using the left lane means that other vehicles can overtake you if they want to. Sometimes people are reluctant to use the left lane because they are worried about changing lanes either for the safety aspect or the risk that they might find themselves boxed in and unable to change lanes. When travelling in the left lane it is almost a certainty that you will eventually come across traffic you have to overtake, for example where traffic is merging from an on ramp or slip road, or traffic is slow.
Anticipation is the most important part of knowing when to change lanes from the left to the middle (or right) in response to events that are happening ahead. Drivers that lack skills or competence tend to be drivers that stick to the middle or right lane.
On a two-lane road, if everyone uses the right-hand lane all the time it effectively converts the road into a one-lane road, and on a 3-lane road, it effectively makes it a two-lane road (often with the middle and left lanes moving at about the same speed).
In the UK there are fines for hogging the middle lane or right lane (overtaking lane) when not overtaking another vehicle. We don't have that in Australia.