1. Well, from this statement, we can only conclude that n is a prime number, since only prime numbers have exactly two positive factors (1 and the number itself). So A by itself is not sufficient.
2. This is a tricky one. Let's take the odd numbers first. They can only have other odd numbers as factors. The difference between two odd numbers will always be even, so odd numbers can be crossed off the list.
Now let's look at even numbers greater than 2. They can have either even or odd factors, but will always have at least two even factors (the number itself and 2). Since the difference between an even number and 2 will always be even, we can also cross this set of numbers off the list. This means that indeed, 2 is the only number to have this property.
Answer B
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