b) in b the number of blocks are 4 and the shaded ones are 2 so the fraction is:

and the diagram will be:
c) in this case the total number of blocks are 5 and the sahded ones are 3, but they are grouped like:

and the diagram will be:
d) in this case we have 6 blocks and 5 shaded and they are grouped like this so:

and the diagram will be: