Trevor was hired to evaluate the ease of use' of the web site for a company called Travel by Knight. Which of the following is one of the elements that he should be evaluating when focused solely on the site's ease of use?

a. The first page is easy to understand.

b. The site makes good use of colour.

c. The site has user-centric privacy controls.

d. Typefaces and font sizes are very readable. 

e. Physical attractiveness.