The use of turbo- prop engine is limited to

Question

 Assertion (A): The use of turbo- prop engine is limited to medium speed applications   

Reason (R): The efficiency of a turbo- prop engine decreases at higher speed.

1. Both A and R are individually true and R is the correct explanation of A
2. Both A and R are individually true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true