Which of the following situations is extraordinarily unlikely?

A) A reliable test is valid.
B) A valid test is unreliable.
C) A invalid test is unreliable.
D) An unreliable test is invalid.

A valid test indicates that it is measuring what it intends to measure, while a reliable test produces consistent results. It is possible for a valid test to be unreliable, in which case it is measuring what it intends to measure but not consistently. However, it is extremely unlikely for a valid test to be unreliable, as the consistency of results is a key component of validity. The other options are more likely, as an invalid test and an unreliable test are both possible and can often occur together.