Some True/False questions are not visible. Usually teachers hides their visibility if they are few in number. Subject Expert recommends them to have more than 70+ questions against the topic and make them public.
Visibility is the ability of one object to "see" or have a reference to another object. TrueView Answer
A designer can describe the design of one or more scenarios of a use case; each of these is called a use case realization TrueView Answer