The diagram shows a summary of photosynthesis.

What substances do each of the letters represent?

a
W is O2; X is H2O; Y is CO2; and Z is glucose.
b
W is H2O; X is O2; Y is CO2; and Z is glucose.
c
W is H2O; X is O2; Y is glucose; and Z is CO2.
d
W is CO2; X is O2; Y is H2O; and Z is glucose.