Mixed aldol reaction

The mixed adol reaction between propionaldehyde and acetone gives an 85% yield of 4-hydroxy-2-hexanone when run in THF at -78 degrees C with lithium diisopropylamide (LDA is a powerful base). The reaction is carried out by first adding the ketone to the base, cooling the solution, and then adding the aldehyde.
Please answer the following:

    a.) Why does this mixed system give essentially a single product?
    b.) Why is there no self-condensation of the acetone?
    c.) Why does the system not rapidly gon on to dehydrate?
    d.) Why is the ketone added to the base rather than vice versa?