Imagine ето as "this is" construction, so it does not change regardless of gender of object, like Shady_arc said. But when they modify a noun, then it means "this (one)" and then it must agree with the noun in gender, number and case. зта is then used for female nouns in singular, and зтот for male singular, and зто for neuter singular. For example if you say this is a cat then you don't need to agree "this" with "cat", they are not connected. But if you want to say this cat is nice then you must agree this and cat because they form one unit. In that case "This cat" will be different from "(of) this cat", "(with) this cat" or "these cats". I hope this helps.
In which of the sentences? The adjectival «это» agrees wuth the noun it modifies in gender, number and case. That's why it becomes эта when acting as a modifier. When «это» acts on its own and is not connected to «кровать» anyhow (apart from being in the same sentence) and does not imply any other noun, it is singular and neuter. More specifically, a subject in all of these sentences is the same:
- Это крова́ть. = This is a bed.
- Это ко́шка / кот. = This is a cat.
- Это учи́тель. = This is a teacher.
- Это учителя́. = These are teachers.
- Это крова́ти. = These are beds.
That is really confusing because you didn't give any examples of the other usage.
A dash in an optional mark in such environment. Still a possibility, mind you! You will see it in similar sentences IRL sometimes.
We occasionally use it to let you better parse the sentence. I feel that a string of nouns might be tricky for an English speaker to mentally cut into segments (I imagine, to you such sentences look like "cat on the bed mine")
Only if you know that otherwise your answer was OK. Also, note that "he" instead of "she" and "law" instead of "low" are not considered typos: if you get a different word, you WILL be marked wrong.
Naturally, we add translations by hand, so we take into account all reports, including those with minor mistakes..
It is not grammatically correct in english. You can say This is my bed. but This bed is mine. There are pairs of possessive determiners and pronouns my/mine, your/yours, her/hers, our/ours and their/theirs. If it is before a noun you use determiner (your) and pronoun after (yours).
In that case you have swapped "this" for "the". The difference is large enough to warrant a different syntax in English and in Russian.
"This bed - it is mine." is perfectly acceptable English and I believe matches the meaning and tone of the Russian statement.
Words ending in -ь (in spelling) can be masculine or feminine. Feminine are a bit more plentiful, and also there are suffixes that make masculine or feminine nouns with 100 % certainty (вечность, относительность, мощность, мудрость are feminine; учитель, выключатель, предохранитель, родитель are masculine).
Other than that, you should just know the words—thankfully, the class is not that big. Masculines within the top 3000 words or so are as follows:
- month names
- день, рубль, ноль, огонь, дождь, камень, корень, пень,
- учитель, родитель, писатель, читатель, преподаватель, свидетель, следователь, покупатель, водитель, двигатель, корабль, руководитель
- гость, парень, король, царь, путь, гвоздь
- секретарь, монастырь, лагерь, словарь,
- стиль, отель, спектакль, контроль,алкоголь, руль, шампунь, портфель, кашель, ноготь
- these animals: зверь, медведь, олень, голубь, лось, гусь, конь, лебедь, журавль, тюлень
No, these just reflect the grammatical gender/number and case of the nouns you attach them to.
To be more exact, adjectives and possessives мой, твой, свой, наш, ваш, чей will match their ending to the noun you attach them to (e.g., мой компьютер, моя кровать, моё молоко).
(его "his, its", её "her" and их "their" do not change and are always used in this exact form.)