Transform the sentence 'Being ill, he could not attend the class' into a compound sentence.

1. ক
   He was ill, so he could not attend the class.
   
2. খ
   As he was ill, he could not attend the class.
   
3. গ
   He could not attend the class because he was ill.
   
4. ঘ
   Since he was ill, he missed the class.