-da

Explanation

1. -da
A connective ending used when an action or state, etc., is stopped and changed to another action or state.

2. -da
A connective ending used when something happens while a certain act is ongoing.

3. -da
A connective ending used when the preceding statement is the cause or reason for the following statement.

4. -da
A connective ending used when more than two facts happen in turns.

Examples
나는 영화를 보다 잠이 들었다
그들은 따로 살다 이번에 살림을 합쳤다
그 사람은 우리 회사에 다니다 다른 회사로 이직을 했다

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