In silicon dioxide $(SiO_2)$:

• A
  Each $Si$ atom is surrounded by four $O$ atoms and each $O$ atom is bonded to two $Si$ atoms.
• B
  Each $Si$ atom is surrounded by two $O$ atoms and each $O$ atom is bonded to two $Si$ atoms.
• C
  Each $O$ atom is bonded to only one $Si$ atom.
• D
  There are double bonds between $Si$ and $O$ atoms.