How to use All Wheel Drive feature for my 2006 ford taurus?

There are 2 Drive option on my 2006 ford Taurus: the first is marked as a bold D the other a shaded D. My owners manuel doesn't say which is for AWD.

Does anyone know?!

All of them are - It's always on.

AWD does not give you a choice to switch to 2wd like 4wd car does. If you get an AWD it is always turning all 4 wheels. This is good for high horsepower cars, or during the winter, because you never have to worry about shifting into 4wd. This is bad for all the times of the year you don't need it because its a waste of fuel and wear and tear on critical drive train parts.