Translation:Where is the yard?
Yes, kanji can help us understand what is being said especially with all the homophones in Japanese but context, position, what a word is doing in a sentence, which particles it is marked by, whether it is modifying another word, grammatical rules can all help us understand and differentiate/eliminate homophones too. In this sentence for instance if にわ was a counter for birds it would be either modifying とり or being used to describe the number of とり, in which case the most likely sentence would be にわのとりは どこ ですか. There's a lot that we can determine even without kanji there to help us out : )
Oh, this is a fun one for the english speakers. Most differences between UK, Canadian, Australian, New Zealand, and US english are no big deal. Everyone gets that a lorry is a truck, and an apartment is a flat. But yard and garden are one of the rare cases where both words have different meanings, depending on who you ask.
the particle wa would never be used in place of the article ni and vice versa. These early lessons have only really established ni as a directional particle I think. So - gakkou ni ikimasu (I go to school) - the specific place you're going to is marked by ni. We've also seen it used for getting in or on transport - ni norimasu - if you think about it this is still directional in a way because you are moving onto or into a vehicle - jitensha ni norimasu (I get on the bike or if you're trying to be more literal I ride on the bike). Certain verbs take ni - ni hairimasu (enter into where the place that you're entering precedes the particle ni) - in this instance it's a set construction. Yet to come up in lessons but you can use ni to say I believe in ... eg. kare ni shinjimasu (I believe IN him - as opposed to kare o shinjimasu - I believe him). You can also use it with shinrai shimasu which means trust so ....... ni shinrai shimasu means to trust in....As for the particle wa - it usually marks the subject of a sentence and is often missing as the subject is often "understood" as being either I (speaker) or you (listener). It can be used to modify a noun to mean - in regards to this... or to add extra emphasis to the subject of a sentence rather than relying on context or as a way to abbreviate a sentence - kyou wa? (how about today), anata wa? (and you/how about you?), ima wa? (and now? meaning (what are you doing) now?) etc. Also in a sentence where you have a subordinate clause - a sentence within a sentence - wa marks the subject of the main sentence and ga marks the subject of the subordinate clause. Ga can also be used to mark the subject of a sentence - its effect is to give extra emphasis to the subject/topic and some verbs or constructions take ga eg. _ga suki/kirai, ____ ga dekimasu etc. Hope this helps. Particles are invaluable! They let you know what everything's doing in a sentence so it's a good idea to get a handle on them early on :)
There's actually an option to switch to a keyboard instead of the word bank (not sure if it's available on the app though). I'm guessing that they do expect that some people will type in their answer - it's just typically inconsistent Duo that's to blame for them accepting kanji in some instances and not accepting (often the very same kanji) in others.