※ Our check while writing this explanation could not fully confirm the published answer; scoring follows IPA's official key.
×Incorrectア
A scroll bar is a component for moving the displayed area of a window or a list up, down, left, or right; it is not a component for entering or selecting a value. It cannot be used to specify the value of the “Type” field itself.
×Incorrectイ
A checkbox lets each item be turned ON or OFF independently, so several items can be selected at the same time. Since “Type” is an exclusive field in which only one of the four values is chosen, a checkbox, which allows multiple selections, would permit input that violates the specification and is therefore inappropriate.
×Incorrectウ
A text box is a component that lets the user freely enter any character string. Using it for a field whose candidates are already fixed as “Planning, Purchasing, Contract, Other” invites typos, inconsistent wording, and values outside the candidate list, and it also makes extra checking processing necessary afterwards. For a field with a fixed set of options, a selection-type component should be used.
○エ
正解The correct answer is エ, “Radio button”. In Table 1 of sub-problem C, the input field “Type” is defined as a field in which only one of the four approval types “Planning, Purchasing, Contract, Other” is chosen. For an input like this, where the options are fixed in advance and exactly one of them must be selected exclusively, a radio button is the most suitable component. Radio buttons in the same group are mutually exclusive: selecting one automatically clears the others, so input errors such as selecting two or more values or writing the value inconsistently are prevented at the level of the component specification itself. Since there are only about four options, all of them can be lined up and seen at once on the screen, which also makes a radio button appropriate.
ここがポイント
Choosing the right GUI component: use a radio button when exactly one option must be chosen from a fixed set of options (exclusive selection), and use a checkbox when any number of items may be selected or when switching something ON and OFF.
For an input field whose candidates are few and fixed, using a selection-type component instead of free entry in a text box prevents inconsistent wording and input errors at the screen-design stage (screen design as a countermeasure against human error).