wn(markdown) {
          return marked.parse(markdown);
        },
        toggleMode() {
          this.mode = this.mode === 'sequential' ? 'random' : 'sequential';
          this.startAllQuestions();
        },
        startAllQuestions() {
          this.fetchQuestions().then(() => {
            this.shuffleIfNeeded();
            this.resetQuiz();
          });
        },
        startWrongQuestions() {
          if (this.wrongQuestions.length === 0) {
            alert("暂无错题可刷");
          