Answer: If A is used to represent a natural number, then 2a must be divisible by 2. According to the meaning of even number, 2a must be even number. This question examines students' understanding of the definition of even numbers. Even numbers are defined according to whether natural numbers are divisible by 2.
Precautions:
Even numbers are numbers divisible by 2. Whether 2a is even depends on the value of a. If a is a natural number, 2a is even. If a is a decimal, 2a is not an even number. For example, a equals even number 8, 2a equals 16, 16 is even number, for example, a equals odd number 9, 2a equals 18, and 18 is even number. When a equals 2.5 and 2a equals 5, 5 is an odd number. The result of algebraic expression is determined according to the situation of letters.
In advanced mathematics, 2a is not necessarily an even number, because even number is defined as a natural number divisible by 2, so it does not include decimals, irrational numbers and so on. So if a is a decimal, 2a is not a natural number, so it is not an even number. If a is a natural number, then 2a is an even number. Only when the definition is very clear can we get the correct result.