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。

    Itzhak Perlman is ____ famous violinist. He was born ____ 1945. He once gave a concert in New York City. Getting on stage was difficult for him ____ he is disabled. The audience sat ____ (quiet) while he made his way across the stage to ____ (he) chair. Then he picked up the violin, ____ (put) it under his chin (下巴) and started to play. But this time, when he finished the ____ (one) part, one of the ____ (string) on his violin broke. ____, he continued to ____ (play) the music. The music he played with three strings sounded even more wonderful than it was played with four strings.

下面是一段有关抗美援朝的文字表述，其中有三处错误。请指出并用相关史实说明错误的原因。
为了抗美援朝、保家卫国，1950年10月，以朱德为司令员的中国人民志愿军开赴朝鲜前线，同朝鲜军民一起抗击美国侵略者。中国人民志愿军同朝鲜军民并肩作战，五战五捷，其中在上甘岭战役中涌现了象邱少云这样的英雄人物。他用身躯堵住敌人的机枪射口，壮烈牺牲。1952年7月，美国被迫在停战协定上签字。
错误 ____；改为 ____。
错误 ____；改为 ____。
错误 ____；改为 ____。

2角=____元

可导函数 y=f(x) 在某点取得极值是函数 y=f(x) 在这点的导数值为 0 的（   ）