feat: 马丽 picks either of multiple correct multiple-choice answers

[toshify]

马丽 sees the multiple-choice exercise screen.
马丽 touches the item under test button and hears the corresponding audio
马丽 sees at least two correct answers
马丽 touches one of the correct answers and sees the celebration state.
马丽 re-visits the exercise and touches the other correct answer, and sees the celebration state.

Requires

• handling of multiple correct multiple-choice answers
• corresponding data-structure