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【多选题】
以下关于java.lang.NullPointerException描述正确的是:A.
public class Test { public void f1() { } } public class Pargoam2 { public static void main(String[] args) { Test t1; t1.f(); } } 运行Program2的main方法时，会发生java.lang.NullPointerException
B.
public class Test { public void f1() { } } public class Pargoam2 { public static void main(String[] args) { Test t1; t1.f(); } } 运行Program2的main方法时，不会发生java.lang.NullPointerException
C.
java.lang.NullPointerException属于Java运行时异常
D.
当一个对象为空是，调用这个对象的实例化方法时，会发生java.lang.NullPointerException
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【简答题】 在单相桥式整流电路中,变压器次级电压 V 2 =120V (见下图),在未接滤波电容 C 时负载两端电压 V L 是多少伏?加了滤波电容并在空载情况下输出的直流电压最大值可达多少伏,此时整流二极管实际承受的反向电压是多大?
【单选题】The example of the man shows an ability to ______.
A.
avoid traffic accidents
B.
judge the good and evil of a person
C.
know about the events that are happening some distance away
D.
sense a danger that will actually happen later on
【简答题】在单相半波、单相桥式整流电路中,加滤波电容和不加滤波电容两种情况下,二极管承受的反向工作电压有无区别?为什么?
【单选题】在单相桥式整流、电容滤波电路中，下列说法正确的是（ ）。【图片】
A.
二极管承受反向电压最大值为输入电压的最大值
B.
若电容为电解电容，其极性应与输出电压极性相反
C.
电路输出电压的最大值为输入电压的有效值
D.
当电容C开路时，各二极管的导通角不变
【简答题】What do most parents expect of their children in preschools? A) The ability to get along with other children B) The to learn what they like C) Enjoyment of free play D) Good academic performan...
【简答题】A．It can affect the ability of finding information. B．It decides the ability of reading newspaper. C．It can affect the ability to earn a living. D．It decides the pleasure of reading.
【单选题】A set of genes play a role in learning to read and do math, but this ability is not just gene-driven,【C1】______schooling and help from parents are also vital【C2】______. Early mathematical ability and ...
A.
as
B.
so
C.
though
D.
if
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