"It is a dog."
Translation:Es ist ein Hund.
The grammatical form that you need in this exercise is called “predicate nominative” in English. It is the situation where the predicate of the sentence (the portion after the verb) is the same as the subject. The best example in English is when you knock at the door and someone calls out to you “Who is there?” and you provide the grammatically correct reply is “It is I”. This is a predicate nominative. Lots of people answer “It is me” which is incorrect in English. The word “me” is objective case. The correct word to use is “I”. Similarly in German when translating “It is a dog” to be grammatically correct, you must recognize that you are in a predicate nominative situation since the subject “It” and the predicate “dog” are the same. You must use the nominative case for the indefinite article. “Ein” is nominative case, i.e. the subject. “Einen” is objective case. Therefore the correct translation of “It is a dog” is “Es ist ein Hund”. I hope I did not make things worse or more confusing. My mother was an English teacher and she yelled very belittling comments at us kids whenever we answered a question with “It is me”.
I just read through that tip, then used control find, and no, einen is not explained in that tip. Ein is mentioned, but I believe the confusion here is when einen should be used. In other words, we're not wondering how ein is used, but what the difference is between ein and einen
This discussion is rather funny, because it reminds me that when I was a child between 4 and 5 yrs old, (born and raised in the USA with American English), I always saw dogs as male and cats as female. It just seemed normal to me. At that time, I even though that it took the two of them to make more dogs and cats.
I have no idea where I got this from, since I was never taught German when I was a child.