Task: Question Answering
Input (English): Problem: a and b can do a piece of work in 10 days and 10 days respectively. they work together for 10 days and b leaves. in how many days the whole work is completed ?
Options: a. 30 days, b. 40 days, c. 50 days, d. 60 days, e. 70 days
Output (English): a