Stephen Yang only smirked at her sister's innocent question because that was the only thing he could do. It was so clear that she was just a bit stronger than his Chrsie so he thought of doing that himself.
But in order to give his sister a chance and motivation to train up, he appointed her as a responsible person in the end. He said,
"Train her and yourself"
'Ttt..t.tttt...train????? Does he want me to teach Chrystal some martial arts?' Cookie Hua looked absolutely confused because all that she could think about at this moment was Chrystal who was so delicate. She wondered how he came up with that stupid decision.
"Okay, I will take care of it" Cookie Hua accepted because she felt like it was going to be fun and adventurous at the same time. As they both were girls, there is nothing to worry about either.