Circle the letter of the phrase that best completes the sentence. 3. If the RuBP consumed in Step I was not regenerated in Step 4 of the Calvin cycle, then

a. CO2 would stop diffusing into the stroma.
b. the cycle would speed up because of an increase in CO2 molecules.
c. the plant cell would lack G3P molecules.
d. the plant cell would stop bonding carbon atoms from CO2 into organic compounds.