How can we define the coefficients a half wave symmetry when n is even?

• A. an=0 and bn=0 and a0=0
• B. an=4/T∫x(t)cos(nwt)dt and bn=0= a0
• C. an=4/T∫x(t)sin(nwt)dt and bn=4/T∫x(t)cos(nwt)dt and a0=0
• D. an=4/T∫x(t)sin(nwt)dt and bn=4/T and a0=0