If I work, then I earn money, but if I'm idle, then I enjoy myself. Either I work or I'm idle. However, if I work, then I do not enjoy myself, while if I'm idle, then I do not earn money. Therefore:
A. I work if and only if I enjoy myself.
B. I work if I earn money.
C. I do not earn money if I'm idle.
D. I enjoy myself if and only if I do not earn money.