Which version of the sentence uses correct parallel structure?
A. Saving is the key to a comfortable old age, and not saving is to be the key to an anxious one.
B. Saving is the key to a comfortable old age, and in not saving is the key to an anxious one.
C. Saving is the key to a comfortable old age, and not saving is the key to an anxious one.
D. Saving is the key to a comfortable old age, and not to save is the key to an anxious one.