When adding up fractions, the idea is to bring them to a common denominator. In our case, the common denominator is 12. So we must amplify each fraction in order to bring its denominator to 12. 1/6 becomes 1*2/6*2 = 2/12. 2/3 becomes 2*4/3*4. 1/4 becomes 1*3/4*3. When we sum them up we get 2/12 + 8/12 + 3/13 or 13/12, which is (12+1)/12 or 12/12 + 1/12 or 1+ 1/12. So the answer is C.