The structure of diborane $(B_2H_6)$ contains

• A
  Four $2c-2e$ bonds and two $3c-2e$ bonds
• B
  Two $2c-2e$ bonds and four $3c-2e$ bonds
• C
  Two $2c-2e$ bonds and two $3c-3e$ bonds
• D
  Four $2c-2e$ bonds and four $3c-2e$ bonds