Missing Watashi from Textbook Translation


I'm using Japanese From Zero 1, though I've already memorized both symbol
libraries and a hand full of Kanji.

I'm at section 3, Q & A E -> J, Group 4.

My issue is that I'm still a beginner and I think it's giving me the wrong
translation.

It wants me to translate the English statement;

> No, it's my friends car.

I translated this as;

> いいえ、わたしのともだちのくるまです。

But the book claims that the translation should be;

> いいえ、ともだちのくるまです。

Which removes わたし. How can it mean My Friend and not just Friend, if I'm not
in the sentence? Is it assumed or is it because the first sentence Asks,

> Is this your car?

It seems like the topic is shifting from My car to My friends car, so
shouldn't I change the topic?

Full Question;

> Is this your car?
>
> Yes, it is.
>
> No, it's my friend's car.
>
> No, it's her car.
>
> No, it's her's.

* * *

Edits: Yes, it's くるま Kuruma ^-^, I was typing too fast.




As taikun said, in normal Japanese you never use a pronoun if it is obvious
for the listener.

This is especially true for first person pronouns (私{わたし}、俺{おれ}、僕{ぼく}、etc.),
because using it too much would be perceived by your listener as if you're
trying to grab the attention (even if you're a gaijin this would be bad for
your [謙虚{けんきょ}](https://thejapanexperience.wordpress.com/2010/02/22/kenson-
kenkyo-modesty/)). So your lesson is very correct in the way that a Japanese
person would not have answered by 私{わたし}の友達{ともだち} in this context.

For further reading on the topic I suggest this article from [Japanese
Ammo](http://www.japaneseammo.com/stop-using-watashi-i-the-real-way-to-refer-
to-yourself/)




It's obvious from the context, so the pronoun is omitted.

