Added "The boy's drawing...".

I guess this happens in the reordering word exercise. It seems they simply concatenate each word in answer and join them with a space ([the], [boy], [is] is joint to form [the boy is]; with the same logic, [the] [boy] ['s] becomes [the boy 's])

I guess Duo has already known about this problem but as it isn't stopping correct answers get accepted, they aren't prioritizing fixing it.