Usages of desu
B: This one is yours.
- That's so, isn't it.
- I see.
neko ga mo inu ga mo suki desu.
bangohan wa nanji gurai desu ka.
kanojo wa, gojussai goro desu.
Using です before から is very formal. We'll learn in a later lesson how to make less formal sentences with から.
Note how this sentence shows how the word 事 is the origin of the verb nominalizer 〜こと.
The particle で functions as a means or method marker here, indicating the manner or state of the document. It is used to ask if being in the form of a copy is acceptable or sufficient for the purpose at hand.
The word issyo is used here to show that the opinions are unified or aligned (held together with the other person).
Most of the time you should use the word 同じ when referring to things that are the same.
benkyoushitara, toshokan ga shizuka desu.
The たら form is ungrammatical here, because the library is quiet is not something that happens after you're going to study.
Both 人気 が ある and 人気 です are correct translations for to be popular.