A. Why do you think some people prefer to be single?

 - I think they worry about losing important things such as grades, careers and so on. ✔  ​

We cannot make a rational decision when we so emotional. 

  => We cannot make a rational decision when we so emotional. ​​​

  => Corrected : The sentences are corrected grammatically.     

And love is the most strange and unknown feeling. 

  => And love is the strangest and unknown feeling. ​​​

  => Corrected : The sentences are corrected grammatically.     

For these reasons, I think some people prefer to be single for their career and life. ✔ ​

B. Make these sentences into English.

-나는 너무 졸려서 일찍 잤다. (I felt very sleepy so I slept early.)

  => I was so sleepy that I hit the sack early.​

  => Your answer is correct but here's another way of saying it.​​​

-내 코트 자락이 못에 걸렸어. (My coattails are hanging on a peg.)

  => My coat was caught on a nail.​​​

  => Corrected : The sentences are corrected grammatically.    

-왜 그녀가 나를 차갑게 대했는지 아니? (Do you know why she was not nice to you?)

​  => Do you know why she gave me the cold shoulder?​​

  => Your answer is correct but here's another way of saying it.