[单选题]
Doubling the diameter of a loop of b(sxdps;k0x1i qq p+8wirezm,q lrws,a* : produces what kind of change on the induce a w:*,ls,mqzrd $emf$, assuming all other factors remain constant?
A. The induced $emf$ is 4 times as much.
B. The induced $emf$ is twice times as much.
C. The induced $emf$ is half as much.
D. There is no change in the induced $emf$.