Firstly, let's understand this function. We're supposed to add 4, 5, and 6 to whatever integer is plugged in, and then multiply the 3 results. It's very useful to know that in any set of, say, 5 consecutive integers, exactly one of them must be divisible by 5. Try it out. Similarly, in the same set of 5 consecutive integers, 1 or 2 of them must be divisible by 4. If the first one is divisible by 4, then the last must also be divisible by 4. If one of the numbers in the middle is divisible by 4, then it'll be the only one. In the same set, 2 or 3 of the numbers will be even. You get the idea.
In this set of 3 consecutive integers, we know that one of them is divisible by 3, and 1 or 2 must be divisible by 2. So if we multiply them all, the result must be divisible by both 3 and 2, or in other words, it's divisible by 6. Thus the answer is C.
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