[单选题]
Materials in which tqe :(1tg406u5r7z7.cil.c emiy vsdbh ezs.she electrons are biygg3a7)j,:ri 2snr)f )ua4r vcn, a bound very tightly to the nuclei are referred to as) f3auj)vbi)arnsg: y i7cn,g,4rra2
A. insulators.
B. conductors.
C. semiconductors.
D. superconductors.
