Task: Question Answering
Input (English): Problem: a person ' s present age is two - fifth of the age of his mother. after 4 years, he will be one - half of the age of his mother. how old is the mother at present ?
Options: a. a. 25, b. b. 40, c. c. 20, d. d. 45, e. e. 28
Output (English): c