[单选题]
In a transformer, if tl57u y tzg9jj8cfl2z(g-jb i0 he secondary coil contains macq( n3xd .3(n)ufiq bore loops than the primary coil t3 qdib(annu)c (f.q x3hen it is a
A. step-up transformer.
B. step-down transformer.
C. either a step-up or a step-down transformer.
D. can not be determined.
