11963
Potassium , rubidium , and caesium react with graphite ; their atoms are intercalated between the hexagonal graphite layers , forming graphite intercalation compounds of formulae MC ( dark grey , almost black ) , MC ( dark grey , almost black ) , MC ( blue ) , MC ( steel blue ) , and MC ( bronze ) ( M = K , Rb , or Cs ) .
 MC, MC
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 MC, MC