Question

An apple a day keeps the doctor away. (Add a suitable question tag​

Answer 1

Answer:

An apple a day keeps the doctor away, doesn't it?

OR  

An apple a day keeps the doctor away, isn't it?  

Explanation:

In the first sentence, the question tag is with respect to what the apple does. In the second, it is with respect to the entire saying taken as one single truth.  

Considering that "An apple a day keeps the doctor away" is a single piece of truth, the second option (isn't it) is better suited.

Answer 2

Answer:An apple a day keeps the doctor away isn't it??

Explanation:In the first sentence, the question tag is with respect to what the apple does. In the second, it is with respect to the entire saying taken as one single truth. Considering that "An apple a day keeps the doctor away" is a single piece of truth, the second option (isn't it) is better suited.

hope it helps you