压油散热器是液压系统中的（）元件。 ["执行","辅助","控制","动力"]
在几何图形上，供给量的变动表现为商品的价格-供给量组合点沿着同一条既定的供给曲线运动。
既能消除嫉妒、疑惑又能排除心底淤塞的音乐作品是（） ["《威廉退尔》序曲","《安魂曲》","《婚礼之日》","《芬兰颂》"]
简述证据保全的意义。
public class X { public static void main （String[] args） { byte b = 127； byte c = 126； byte d = b + c； } } Which statement is true？（） [" Compilation succeeds and d takes the value 253."," Line 5 contains an error that prevents compilation."," Line 5 throws an exception indicating “Out of range”"," Line 3 and 4 contain error that prevent compilation."," The compilation succeeds and d takes the value of 1."]
波前和射线两者之间的关系如何？
