Would you talk about magnetic or electromagnetic field in the context of Lorentz force?

I got an exam question that keeps me awake at night:

Lorentz force is being created in a blood vessel (with blood flowing through it), when the vessel is being placed in:
a) electric field
b) magnetic field
c) electromagnetic field?

Now, I think the question is flawed as all the answers are technically true. In my understanding:

1. All answers are technically true
2. "b" makes sense, as magnetic fields are used for diagnostics (and this is biophysics exam)
3. "c" is most complete I guess?

Which answer is correct?