This question's explanation and your answers so far.
Mさんの部署では，図に示すような，PC2台（PC1とPC2），サーバ1台とプリンタ1台を，ハブ1台と4本のケーブルa～dでつないだLANで構成されるシステムを使っている。 このLANに接続されているプリンタは，プリントサーバ機能を有しており，PCから直接プリンタに出力できる設定になっている。ある日，MさんはPC1からプリンタに出力を行ったが，出力できなかった。前日に同じ処理を行ったときは，出力できていた。 なお，各機器と各ケーブルの接続箇所については，ソケットの不具合は機器側の障害，コネクタの不具合はケーブル側の障害として切り分けられるものとする。また，障害が複数箇所で同時に発生する可能性はなく，PC1では障害が発生していないものとする。 障害の原因と考えられる構成要素は，LANを構成するPC2，サーバ，プリンタ，ハブとケーブルa～dの八つの中に幾つあると考えられるか。
Answering 1 is the number you get if you jump to the conclusion that, since nothing was printed, the printer itself must be at fault. However, the same operation did print successfully the previous day, which shows that not only the printer but also a poor contact or a break in the hub or in either of the two cables along the way would produce the same symptom. Every element on the path is equally suspect, so the candidates cannot be narrowed down to one.
Answering 2 is the number you get if you count only the devices (the printer and the hub) and forget the cables, or conversely count only the two cables and forget the devices. This question is premised on an explicit separation in which a socket defect is a fault on the device side and a connector defect is a fault on the cable side, so both the devices and the cables must be counted as separate candidates.
Answering 3 is the number you get if you over-extend the condition that no fault has occurred in PC1 and also drop the cable attached to PC1 from the candidates. What is guaranteed to be fault-free is only the device PC1 itself; the cable connecting PC1 and the hub (a loose connector or a break) can still be the cause, so it must be kept among the candidates.
正解 Since output cannot be sent from PC1 to the printer, the cause is limited to the components on the communication path along which PC1 sends data to the printer. The printer has a print server function and is configured so that output can be sent directly from a PC, so the path is: PC1 → cable (between PC1 and the hub) → hub → cable (between the hub and the printer) → printer. Faults do not occur at several points at the same time, and the question states explicitly that no fault has occurred in PC1, so the candidate causes are what remains on the path, namely (1) the cable connecting PC1 and the hub, (2) the hub, (3) the cable connecting the hub and the printer, and (4) the printer itself — four items. Note here that, because of the rule that a defect in a socket (the receptacle on the device side) is treated as a fault of the device and a defect in a connector (the terminal on the cable side) as a fault of the cable, devices and cables must each be counted as separate, independent candidates. Of the eight items listed in the question (PC2, the server, the printer, the hub, and cables a through d), PC2, the server, and the two cables that connect them to the hub take no part in this communication path, so they drop out of the candidates. Therefore the number of components that can be considered is four, and the correct answer is エ.