While it may be "technically wrong" to use the word platypi because it is linguistically unrelated. It is also technically right because it was a loan word brought into English where the rule of switching -us to -i to make it plural already existed. Think of the word Mongoose for instance. Mongoose is unrelated to Goose but we still refer to more than one mongoose as mongeese because the pluralization by switching -oo- to -ee- already existed.
But it has been Latinized, has it not? It ends in "us" not "oς"
Wikipedia: 'There is no universally agreed plural of "platypus" in the English language. Scientists generally use "platypuses" or simply "platypus". Colloquially, the term "platypi" is also used for the plural, although this is technically incorrect and a form of pseudo-latin;the correct Greek plural would be "platypodes".'
The exception of platypuses was also my first thought on seeing this sentence... In general, it would be interesting if instead of translating phrases, the exercise would be a questions that you had to answer : for example, to learn the world 'forest' the questions could be: "Where do many trees grow?" or something like that...? Does anyone have thoughts about this?
If you have an account on Vortaro.net, you can see a few definitions. It primarily means "to put something aside" or "to deposit". So a ship could drop an anchor ("ŝipo demetas ankron") or a river could deposit gold flecks ("la rivero demetas orerojn"). Those are both examples out of Vortaro.net.
Well, yes if you "lay" something... Demetas really means to put something. So, you might put your keys on the table before a nap: Mi demetas miajn ŝlosilojn sur la tablo antaŭ dormeto. There are some other examples above in the thread, where I've linked to the Esperanto definition.
That's "lie down", not "lay down".... (pet peeve)
In Esperanto, it's kuŝiĝi. (And once you have lain down and are lying, that's kuŝi.)
And "lay" as in "put something onto a surface so that it lies there", as in "lay a shirt on a bed", would be kuŝigi or more generally meti ("put").