※ Our check while writing this explanation could not fully confirm the published answer; scoring follows IPA's official key.
×Incorrectア
The theme and item terms, collection and fee, are right, but it has only three terms and lacks "Company X" to limit the manufacturer. Many off-target pages, such as collection fees for other makers' PCs, will also match, so the narrowing is weak.
×Incorrectイ
Its theme term is "model", which does not match the collection that (1) and (2) ask about. In addition it has only three terms and no "Company X" to limit the manufacturer, so it misses on both theme and target and cannot narrow down to the desired information.
○ウ
正解In an AND search, the results are narrowed to only those pages that contain every space-separated term. The more precisely you combine a term that limits the target with terms that express the theme, the closer you get to the information you want. Items (1) and (2) of [The results Mr. A looked up] concern the fee for collecting equipment made by Company X, so the best search terms are the four words that limit the manufacturer (Company X), name the equipment (PC), express the theme (collection), and express the item of interest (fee). Choice ウ, "Company-X PC recycling fee", satisfies all four. Adding "Company-X" as a separate term in particular limits the target to Company X products and excludes the other manufacturers' pages that "PC recycling fee" alone would pull in, so it narrows down to the desired information most efficiently. Note that ア and イ have three terms while ウ and エ have four, and only ウ matches the content of (1) and (2) (Company X / PC / collection / fee) exactly, with nothing missing or extra.
×Incorrectエ
Limiting the target to Company X's PCs with "Company X" and "PC" is good, but the theme term is "model", not the collection that (1) and (2) deal with. Because the theme does not match, it cannot narrow down to the desired information about collection fees.
ここがポイント
An AND search (space-separated) narrows the results to only those pages that contain all of the specified terms. The key to narrowing efficiently is not the number of terms in itself, but how precisely you choose the term that limits the target and the terms that express the theme (specificity and relevance).
When designing a search string, combining concrete terms that bear directly on your goal, with nothing missing or extra, such as manufacturer (Company X) + equipment (PC) + theme (collection) + item (fee), lets you reach the desired information efficiently. Note too that the space between terms is the AND syntax, so writing "Company-XPC" as one run makes it a single term and changes the meaning.