Electromotive force and potential difference — practice question

What does electromotive force (e.m.f.) mean?

• A$\frac{\text{charge}}{\text{work done}}$
• B$\frac{\text{charge}}{\text{time}}$
• C$\frac{\text{work done}}{\text{charge}}$
• D$\frac{\text{work done}}{\text{time}}$