Nicole Campbell has finished designing a website for the travel company that she works for. She now needs to test its usability. Which of the following according to usability expert, Jakob Nielsen, should Campbell most likely do$?$

A$.$ Get an expert to run through the website

B$.$ Interact informally with people to know preferences

C$.$ Take note of what users feel they can do on the site

D$.$ Observe and examine people use the site

E$.$ Use a questionnaire to track people's opinions