Which of the following is an example of an observable verb suitable for a…

A behavioural (instructional) objective, per Robert Mager's criteria, must be written using an action verb that names a directly observable and measurable student behaviour — something an outside observer can see or hear the learner do, and can count or verify. Verbs that name an internal mental or affective state (thinking, knowing, valuing) cannot be used, because no observer can directly witness a mental state occurring; it can only be guessed at indirectly.

Checking each option against this observability test:

• List — names a learner physically or verbally producing a set of items; an observer can watch the list being written or spoken and count the entries. This is a directly observable, measurable action.

• Understand — names an internal cognitive process of grasping meaning; the process occurs inside the learner's mind and cannot itself be seen.

• Know — names information being held in memory; possessing information is a mental state, not an outward action.

• Appreciate — names an internal attitude of valuing something; it is an affective state, not an observable act.

Cross-check: could a teacher construct an assessment item that directly counts an occurrence of the behaviour named by each verb? Only for List can this be done immediately, by counting the items produced. For Understand, Know, and Appreciate, the verb would first have to be translated into some other, more concrete action (such as "define", "identify", or "select") before it could be assessed at all — confirming that List already names a directly observable, measurable behaviour.