[单选题]
Materials in which the elecb2;a3i+7bd:ptcn 8 cns1y/v2ye i pc ztrons are b u 6ds+8lt1dz08l n+8ktst cvfound very loosely to the nuclei and can move about freely within thu6+cdl +nz8v tt 8k8s1fld0s te material are referred to as
A. insulators.
B. conductors.
C. semiconductors.
D. superconductors.