"Aamir's father is writing a book."

Translation: आमिर के पिता एक किताब लिख रहे हैं।

[P.ep.e]

I wrote आमर के पिता किताब लिख रहे हैं but it was not accepted. Why is एक necessary here?

[Beth205297]

I also think Duolingo has shown itself to be fickle on numerous occasions. I also wrote "आमर के पिता किताब लिख रहे हैं " and it WAS accepted.

But my question is this: why is"हैं" used here instead of "है"? Aamir, father and book are all singular.

[P.ep.e]

It's the plural of respect for Aamir's father. That's why you write रहे and not रहा. Actually, रहे है gets corrected automatically by the Google keyboard because it's a grammatical error.

[bharathwaaj]

Bcos the sentence contains "a" book

[JamesNorth68358]

Why are these kind of questions in the comparison module? Am I missing something?