本試卷共有30題多選題，每題有一個（含）以上的正確選項。各題填答的選項必須完全符合正確項，答錯沒有倒扣，若有任一選項不符合則該題得分為零。

1. Suppose that problem $L_1$ is polynomial-time reducible to problem $L_2$. Which of the following statement(s) is(are) correct?