You have to love the examiners' simplicity, not specifying the type of aircraft. Or maybe they did and its not included in the feedback?
Which TWO instruments are adversely affected by an electrical power failure in flight?:
A. ASI
B. Magn. compass
C. DI
D. AI
E. CDI
On an aircraft like the older 747s with servo driven main instruments the answer is "all" but one has to assume something so I will assume they are talking about a light aircraft. On such an aircraft:
- the ASI has no power supply, it is not affected
- the direct reading magnetic compass has no power supply, but its reading is affected because the deviation correction is done with all power supplied, and therefore it may be incorrect if the electrical power fails. If the compass is remote reading it will require power and therefore be affected.
- the DI is air driven
- the AI is air driven
- the CDI (if it has one) is powered
and therefore I would go for B and E.