In Categorizing Instruments as Either Speed Versus Power, a Power

In categorizing instruments as either speed versus power, a power test means :

A) the examinee's "power" is measured by the number of items answered correctly.
B) the instruments measure the more difficult achievement areas.
C) the instruments are highly rated by experts in the assessment field.
D) the items vary in difficulty, and more credit may be given for more difficult items.