Input Value Out of Range

Wonder with the request. "If the score is out of Range, print an Error". How to get the condition out of range if the following variables are >= 0.9(A) and < 0.6(F).

Write a program to prompt for a score between 0.0 
and 1.0. If the score is out of range, print an 
error. If the score is between 0.0 and 1.0, print 
a grade using the following table:
Score Grade
>= 0.9 A
>= 0.8 B
>= 0.7 C
>= 0.6 D
< 0.6 F
If the user enters a value out of range, print a 
suitable error message and exit. For the test, 
enter a score of 0.85.