阅读理解。

    Many young students consider their friends as the most important people in their lives. They believe that their family members, especially their parents, don't know them as well as their friends do. In large families, it is often for brothers and sisters to fight with each other and then they can only go to their friends for advice. It is very important for young students to have one good friend or many friends. Even when they are not with their friends, they usually spend a lot of time talking among themselves on the phone. This communication is very important in children's growing up, because friends can discuss something difficult to say to their family members.

    However, parents often try to choose friends for their children. Some parents may even stop their children from meeting their good friends. The question of “choice” is an interesting one.

    Have you ever thought of the following questions?

    Who chooses your friends?

    Do you choose your friends or your friends choose you?

    Have you got a good friend your parents don't like?

阅读下列材料：
材料一：卫鞅曰：“治世不一道，便国不法古（治理国家不能按照死板的方法去做，要灵活地根据实际情况变通）。故汤武（古代的好国王）不循古而王，夏桀（古代的坏国王）不易礼而亡。反古者不可非，而循礼者不足多”。孝公曰：“善。”以卫鞅为左庶长，卒定变法之令。
                                                                                                                                                                ──司马迁《史记·商鞅列传》
材料二：秦王扫六合，虎视何雄哉！挥剑决浮云，诸侯尽西来。  
                                                                                                                                                               ──李白
回答：
（1）根据材料一回答：商鞅认为国家必须变法的理由是什么？（在材料中找答案）
（2）商鞅变法有什么历史作用？
（3）根据材料二回答：“秦王”是谁？他最大的历史功绩是什么？