When we add a node on the left branch of a ____ node, the node is automatically balanced.

____________________ tools can make a computer easier to use for people who have disabilities or special needs.

Fill in the blank(s) with the appropriate word(s).

Which of these is NOT one of the attributes the author says may be found in definitions of usability:

a. Learnable b. Efficient c. Habit forming d. Delightful