Its great that duoLingo has a Czech course. Its motivating me to start studying again (felt I got to a comfortable level a few years ago but my Czech has degraded since then).
In my opinion, when translating the phrases, there is too much stress put on using the correct article (ten/ta/to). In colloquial Czech, "ten, ta, to" is often left out of sentences, unless you want to specify something. For example, when ordering something in the shop, you may need to make it clear that you want a specific piece out of many (Chtel bych ten kousek). On the other hand, I realize that for a beginner its important to understand that all nouns have genders (to know which adjective form and declination).
In this case, I feel like the translation is really awkward. Why cant you see dogs? I feel that many of the exercises require a literal translation, which may not often be that practical. In the real world, one might say they saw several dogs in the field, but the friend would reply with "I don't see them" (Nevidim je).