Let's eliminate the options and reach the correct one-
(A) No attempt was made in the survey to determine whether the teachers who received questionnaires had any previous experience with microcomputers --Just because they had experience doesn't mean it was a good experience and it cannot for sure imply that it would propel their interest in microcomputers
(B) Teachers who are interested in microcomputer technology were more likely than others to complete and return their questionnaires.--In the last line of the paragraph it's given: "who responded to survey questionnaires expressed a high level of interest in microcomputers". Thus, the interest word in the option and the line co-incides and does look like a close match
(C) Questionnaires were sent to teachers without regard to their areas of subject-matter expertise or teaching experience.-- Not helpful

(D) There have been several important developments in the classroom applications of microcomputer technology since the survey results were tabulated.--Not relevant
(E) The survey was conducted as part of a marketing study by a company that manufactures and sells microcomputers.--Helps but not as much as option B