-그 쌍둥이들은 아주 사랑스럽다. Those twins are so adorable. ✔ (Punctuation)​

-그녀는 너무 잔다. She sleeps too much. ✔ (Capitalization) ​(Punctuation)

-난 상당히 두려워. I am pretty afraid see you tomorrow. ✔ (Punctuation)​​

-그 업무는 어려웠지만 어떻게든 우리는 그것을 끝냈다.The work was difficult, but we ended it somehow. -> The task was difficult, but somehow we finished it.​ (Punctuation)​​

-그들은 조심스럽게 소포들을 봉인했다.They carefully sealed the package. ✔(Punctuation)​​

-Sarah 화가 나서 문을 쿵 하고 닫았다.Sarah got angry and ran into the door. -> Sarah was so angry that she slammed the door shut.

=> Your sentence has a correct grammatical structure, but this has the correct usage/ expression.

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