Which one of the following could be a transition element?
- Amelting point $114\,^{\circ}\text{C}$, density $4.9\,\text{g cm}^{-3}$, purple, electrical conductor: no
- Bmelting point $659\,^{\circ}\text{C}$, density $2.7\,\text{g cm}^{-3}$, grey, electrical conductor: yes
- Cmelting point $1677\,^{\circ}\text{C}$, density $4.5\,\text{g cm}^{-3}$, grey, electrical conductor: yes
- Dmelting point $3727\,^{\circ}\text{C}$, density $2.3\,\text{g cm}^{-3}$, black, electrical conductor: yes