[单选题]
In a transformer, if the secondary coil co qbx,qrr 4v03vntains more *+xttr(u/)l sa sy;gk loops than the primary coil then it *glxu sa(kt; y+st/)ris a
A. step-up transformer.
B. step-down transformer.
C. either a step-up or a step-down transformer.
D. can not be determined.
