A : I feel English is more difficult language than Korean. 

=> I feel like English is a more difficult language to learn than Korean language.

=> Corrected : The sentences are corrected grammatically. ​

​

      Because I'm Korean. So I'm familiar with Korean grammar system. ✔

     When I study English, I should study unfamiliar and new grammar system. 

=> ​When I study English, I must study about an unfamiliar and new grammar rules.

=> Corrected : The sentences are corrected grammatically. 

​

     That's why what I Feel.

=> That's what / how I feel.

=> Corrected : The sentences are corrected grammatically.  

B : 

- He painted and plastered.

=> He painted and hung wallpaper.

=> Corrected : The sentences are corrected grammatically.  

- Would you change the phone to your mother?

=> Would you put your mother on the phone.

=> Corrected : The sentences are corrected grammatically.  

- Our company should fire 100 employees because of the recession.

=> We have to cut 100 workers because of the economic slowdown.

=> Corrected : The sentences are corrected grammatically.  

    ​