is this reversible

"a dos is a mamamal"?
1. its false
2. true, a animal is a dog if (and only if) it is a mammal
3. true, an animal is a mammal if (and only if) it is a dog
4. true, if an animal is a dog, then it is a mammal

4 is true.

To determine if the statement "a dog is a mammal" is reversible, we need to check if both parts of the statement are equivalent and can be switched around.

The given statement is: "a dog is a mammal". Let's assign the following variables:
- D: a dog
- M: a mammal

Now, let's examine the options one by one:

1. "It's false" does not provide any explanation or reasoning, so we cannot consider this as a valid answer.

2. "True, a dog is a mammal if (and only if) it is an animal." This statement suggests that if an animal is a dog, then it must be a mammal. However, it doesn't cover the case where an animal is a mammal but not a dog. Therefore, this option is not a valid reversible statement.

3. "True, an animal is a mammal if (and only if) it is a dog." This statement suggests that if an animal is a mammal, then it must be a dog. However, it doesn't cover the case where an animal is a dog but not a mammal. Therefore, this option is not a valid reversible statement.

4. "True, if an animal is a dog, then it is a mammal." This statement suggests that if an animal is a dog, it must be a mammal. This is a valid reversible statement since it covers both cases of an animal being a dog and a mammal.

Therefore, the correct answer is option 4: true, if an animal is a dog, then it is a mammal.