Answer:
The best way to combine the two sentences is option ‘B’- My mother, who was leaving, asked me to prepare dinner for my brothers and sisters.
Step-by-step explanation:
Here ‘who’ is the relative pronoun referring back to the ‘mother’, who was leaving. Arranging the words in this pattern, using the relative pronoun ‘who’ to make it clear who was leaving, adds clarity to the sentence making the reader understand that as the mother was leaving, she asked the narrator to prepare dinner for the narrator’s brothers and sisters. There was probably no one else to do so.