Which is correct for the structure of diborane ?
A. It contains four `(2c, 2e)` covalent bonds and two `(3c, 2e)` covalent bonds.
B. It contains three `(2c, 2e)` covalent bonds and three `(3c, 2e)` covalent bonds.
C. It contains two `(2c, 2e)` covalent bonds and four `(3c, 2e)` covalent bond.
D. It contains six `(2c, 2e)` covalent bonds.