Answer: S. (M,S)
Step-by-step explanation:
Because if you have a Periodic Table you can see that:
S is {W in the periodic Table} (ᴇʟᴇᴍᴇɴᴛ- Tungsten) and
M is {Cr in the periodic table} (ᴇʟᴇᴍᴇɴᴛ- Chromium) they are both in the same group. Hope this helps. :))