Here
http://www.japan-activator.com/en/lesso ... icle/id/88the text says:
Quote:
Below is an example in the polite form of the past, and then in the plain form.
彼女は野菜を食べ終わった。
彼女は野菜を食べ終わりました。
As you can see, the first one is in plain form, and the second is in polite form.
I think the order is wrong here, the next section have the same sentence
Quote:
Here is an example with the use of the “-te iru” form, first in the polite form and then in the plain form:
一雄さんはまだ新聞を読み終わっていません。
一雄さんはまだ新聞を読み終わっていない。
And here, the order is correct.