Using progressive when connecting verbs


When connecting two progressive actions, are you supposed to connect them
using progressive in both or only the last one, as tense should be determined
by the last verb?

Example: He was sitting in the classroom, reading a book.

彼は教室にすわって本を読んでいた。

or

彼は教室にすわっていて本を読んでいた。

Thanks in advance




Both of these would not express progressive actions. When you connect verbs
with て-form, it would mean you finished the first action, then did the second
action. 座っていて would be ungrammatical because you imply a progressive action is
already done. Instead, for progressive actions, you would add ながら to the end
of the ます-stem of a verb.

彼は歩きながら携帯をいじっていました。  
He was messing with his phone while walking.

For your example, however, this gets a bit more complicated. Sitting in
Japanese is an instantaneous action, not a state. While you can say you were
"sitting while talking" in English, 座る means the action of sitting down and is
instantaneous. You cannot "read a book while performing the action of sitting
down". Instead, you would "sit down, and then read a book".

So, instead of:  
彼は座りながら本を読んでいた。X This is incorrect

you would say:  
彼は座って本を読んでいた。  
He sat down and read a book.

