汽车由静止开始运动，若要使汽车在开始运动的一段时间里保持匀加速直线运动，则必须（   ）

    Winter is around the corner, and most plants are losing their ____ （叶子）. However, bamboo doesn't. ____ (相反), bamboo stands straight and grow fast. Chinese people say that this is bamboo's ____ (精神). It is ____ (勇敢) enough to overcome difficulties.

    Because of this , the Chinese really love bamboo. They call bamboo, along with the pine tree and the plum blossom, the "three cold-resistant ____ (朋友) of winter.

    Bamboo is a common plant all around China. It has many uses in our  ____ (日常的) life. Chinese people learned to use bamboo to make ____ (筷子) ,baskets and even furniture a long time ago. Bamboo is ____ (使用) to cook all kinds of food. Bamboo is also the main food of the giant pandas.

    Bamboo is also very useful in art. Because bamboo is hollow inside, it's a good choice for people to ____ (制作) different things. It's clever to make ____ （音乐的） instruments. There are many kinds of bamboo flutes all over the world.

阅读下列材料：
材料一  200多年来，浩瀚的太平洋并未阻断中美两国人民的交流合作，中美两国人民相互学习、相互帮助，谱写了世界不同文明相互借鉴的美好篇章。自1979年中美建交28年来，两国关系曾历经曲折，但总体上保持了稳定发展的大方向，给两国和两国人民带来了巨大利益。
材料二 为增进中美两国青年以及教育界的相互了解，我高兴地宣布，中方决定邀请100名耶鲁大学师生今年夏天访问中国……“长江后浪推前浪，世上新人换旧人。”青年人是世界的希望和未来，青年有着蓬勃向上的生命活力和无穷的创造力。
请完成：
（1）结合材料和所学知识，谈谈在新中国成立初期，美国对中国采取了哪些敌对行动？
（2）请用史实说明，20世纪70年代中美两国关系发生了什么重大变化？
（3）作为一名中学生，请你就中美两国关系的发展前景，谈谈你的感想。