this is vs. this

1. In Russian you express the phrases this is, that is, these are, with the single form это.
2. In English and in Russian we use demonstrative adjectives to point to specific items in relation to ourselves. For example, to indicate a specific book that I want you to look at, I will point to the book and say "I like this book". And you might reply, "I don't like that book".
3. The words "this" and "that" are demonstrative adjectives (i.e. they demonstrate or indicate nouns).
4. As in other situations when a word is associated in some way with a noun, in Russian that word must agree with the noun in gender, number and case.
5. This is the reason why in Russian there are four forms for the demonstrative adjective:
   этот - masculine. Этот студент.
   эта - feminine. Эта студентка.
   это - neuter. Это письмо.
   эти - plural. Эти газеты.