“维护国家安全”的有关知识，正确的是（    ）
①关系着整个国家和民族的生死存亡
②是每一个公民的法定义务
③要求公民积极配合国家安全机关工作，为其执行公务提供便利条件
④包括国家主权领土不受侵犯，国家秘密不被窃取、泄露和出卖以及社会秩序不被破坏

阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

    It was a very special day because Dylan Terry came to the West EndChildren's Home! Dylan Terry is my favorite ____ (sing). I like him because he sings ____ (wonderful), he’s cute and he helps the kids alot.

    We ____ (stand) near the door, waiting for him.Everyone was very excited. Finally, he    arrived ____ shook hands with us. He was so nice! He sang several songs for us. Some of us evenstarted dancing ____ he was singing. We were having a great time!

____ our surprise, Dylan joined us for lunch. Hebrought us ____ big cake. Everyone ate some and ____ was delicious. While we were eating, Dylantold us many interesting ____ (story) about himself. I never thought I couldtalk to my favorite pop star. It was just like a dream. I ____ (remember) this unforgettable experienceforever.

依次填入下列各句横线处的成语，最恰当的一组是(　　)

①一个企业要摆脱困境，就必须在激烈的市场竞争中大胆改革，锐意进取，勇于创新，克服________的保守思想。

②现在还有很多司机不吸取血的教训，仍然酒后驾车，对这种________的行为，公安部门更应该加大惩处的力度。

③报载，最近某贪官在法庭上受审时，竟然要求法官放他一马，情愿不做官，回家去种田。这种________真是可笑之至。

现在的物理学中加速度的定义式为a= $\frac{v_t-v_0}{t}$ ，而历史上有些科学家曾把相等位移内速度变化相等的单向直线运动称为“匀变速直线运动”，现称“另类匀变速直线运动”，“另类加速度”定义为A= $\frac{v_t-v_0}{s}$ ，其中v₀和v_t分别表示某段位移s内的初速度和末速度．A＞0表示物体做加速运动，A＜0表示物体做减速运动．则下列说法正确的是（   ）