Multistage/cascaded refrigeration system

[ank_gl]

i am not getting what is the difference between a multistage refrigeration system and a cascaded refrigeration system. i know why staging refrigeration is used.
1# to achieve higher pressure ratio with two or more compressor or multi staging in compressors, thus increasing volumetric efficiency.
2# to get efficient results in wider temperature ranges.

So far, i am confused in following situations.
A#multi staging might refer to refrigeration in 2 cycles with a common heat exchanger(between evaporator for upper cycle and condenser for lower cycle) with same working fluid(refrigerant)
B#multi staging might refer to use of a multistage compressor in a single cycle
C#cascade refrigeration system might refer to refrigeration in 2 cycles with a common heat exchanger(between evaporator for upper cycle and condenser for lower cycle) with different working fluid(refrigerant).

B is out of question, i am confused between A and C, the numerical problems states so. in multi staging, same refrigerant is used and the temperature range is like -20C to 35C and in cascaded numerical, different refrigerants are used, and temperature ranges are wide, -70C to 40C, but then in some other book, i found it all being mixed up, i am totally confused now.

 

[ank_gl]

anyone?? i m totally confused, professor won't let me go ahead until i clear this up

 

[ank_gl]

noooooooooo, can't anyone help