CORRECT!

Quite simply, the attitude indicator is where everything starts. It gives the most immediate indication of a change in the aircraft's attitude. When a change in the aircraft's attitude is needed, that change should be initiated by first referring to the attitude indicator while scanning the other instruments to establish the attitude change. Once the proper attitude change is established, other instruments become primary, depending on the desired maneuver.

When establishing a level standard rate turn, first roll into the turn with reference to the attitude indicator and establish the approximate bank angle on the AI for a standard rate turn. You should continue an instrument cross-check while establishing the turn. Once the turn has been established, the turn coordinator would become primary for maintaining a standard rate turn, while continuing your instrument cross-check.

Answer b) is incorrect because the heading indicator give an indirect indication of bank angle, depending on how fast it is spinning, but would not be considered primary for establishing a standard rate turn. Answer b) is incorrect because the turn coordinator becomes the primary bank instrument only after the standard rate turn has been established.