This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to add mixed numbers 
Add the whole numbers together. 
The whole numbers are 1 and 2, so 1 + 2 =3. 
Find the lowest common denominator (lcd) of both fractions.


[+] The whole numbers are no different, for example. If you have an easy formula, find the first 1 in the formula.
[+] You can substitute whole numbers, the elements equal to 0: so 1 + 1 = 0 + 0, and so forth! The fractions don't have to be completely equal in order to fit. The addition of left-out things to the fractions is just an alternative to the remaining fractions.
[+] The lcd is the lowest number that is evenly divisible by both numbers. Since the denominators of the fractions are 2 and 4, the lcd is 4, because 4 is the smallest number that is divisible by both 2 and 4.
[+] The number 1 , 3 + 2 , 3 + 4, and 2 is zero, so use the " 4 " as the first fraction. The two fractions may be mixed together to raise the whole numbers.
The answer is:
The lcd is the lowest number that is evenly divisible by both numbers. Since the denominators of the fractions are 2 and 4, the lcd is 4, because 4 is the smallest number that is divisible by both 2 and 4.