The structure of diborane (${\text{B}}_2{\text{H}}_6$) contains:

1. A
   four $2c-2e$ bonds and two $3c-2e$ bonds
2. B
   two $2c-2e$ bonds and four $3c-2e$ bonds
3. C
   two $2c-2e$ bonds and two $3c-3e$ bonds
4. D
   four $2c-2e$ bonds and four $3c-2e$ bonds