解决选择声调问题

src/views/exercise_questions/preview/ChooseTonePreview.vue

@@ -106,6 +106,7 @@ export default {
   },
   methods: {
     chooseTone(item, value, i) {
+      if (this.select_item_index !== i) return;
       if (!this.active_letter && this.data.property.answer_mode === 'label') return;
       item.user_answer[item.item_active_index].select_tone = value;
       if (this.data.property.answer_mode === 'label') {