Answer: First, we can simplify 1/6 and 3/6 by finding a common denominator of 12:
1/6 = 2/12
3/6 = 6/12
Now we have:
2/12 + 6/12 + 1/12
Combining the numerators, we get:
9/12
Simplifying this fraction by dividing the numerator and denominator by their greatest common factor of 3, we get:
3/4
Therefore, the answer is C. 9/12.