[单选题]
Materials in which the electrons are bound very y9lkzi (dkqhv09diy bwq,b* zn931y )loosely to the nuclei7k6eeo1 k(69lb7ovd li nl*nr and can move about freely within the ma 1k7ei6 7bolrdnln9 (kvo6e*lterial are referred to as
A. insulators.
B. conductors.
C. semiconductors.
D. superconductors.
