C is the correct option.
For the part a.) There is no join symbol after part.
Fort part b:) after finding Red products say R1,R2,R3 we are just doing a cross prodcut with other tables.So there is no condition which says pick only supplier matching with R1,R2,R3
C:) First we filter Red product Id. R1,R2,R3,then we get the Sid supplying those Parts and then we get names of those IDs.
So c is corect option here