[单选题]
Materials in which the 2;qx, )nsnqg ueleex0j;4 ht :2zmydb9xrjeq .7t ctrons are bound very loosely to the nuclei and can move about freely within the material are rx9y4exz b 7.hjjd:qe mr t;t20eferred to as
A. insulators.
B. conductors.
C. semiconductors.
D. superconductors.
