Answer:
a) no sharps or flats
b) F#, C#
c) B♭
d) F#, C#, G#, D#, A#, E#
e) F#, C#, G#, D#
Explanation:
There is a certain rule for finding what's in a key signature:
Firstly, memorize the fact that C Major has no sharps or flats, and F Major contains a B♭.
For sharps (#), Count 1 note behind the given letter:
Ex. E Major -> D (indicator letter)
Now follow this pneumonic device "Fat Cat Go Down Alley Eating Bolagna" for the order of sharps, FCGDAEB
The order of sharps is indicated by the letter that you counted back from the original key. Simply follow the order of sharps until you've reached your 'indicator letter'
Ex. E Major -> D (indicator letter) so the order of sharps is FCGD, or F#, C#, G#, D#