this.splitSentence(exercise.sentence,boldWordIndex)

splitedSentence(sentence,index) {
        var splitedSentece = sentence.split(" ");
        var slice1=splitedSentece.slice(0,index);
        var slice2=splitedSentece.slice(index,index+1);
        var slice3=splitedSentece.slice(index+1,splitedSentece.length);
        return [slice1.join(" "),slice2.join(" "),slice3.join(" ")];
}