题目内容
（请给出正确答案）
类Teacher和Student都是类Person的子类。
Person P;
Teacher t;
Student s;
P,t和s都是非空值
if(t instanceof Person){s=(Student)t;}
这个语句导致的结果是______。
A．将构造一个Student对象 B．表达式合法
C．编译时非法 D．编译时合法而在运行时可能非法
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更多“类Teacher和Student都是类Person的子类。 …”相关的问题
A.编译时正确，但运行时错误
B.将构造一个Student对象
C.表达式是错误的
D.表达式是合法的
A.编译时正确，但运行时错误
B.将构造一个Student对象
C.表达式是错误的
D.表达式是合法的
A.What time is it
B.What day is today
C.How long will it last
D.How often
Janet, ______was read by the teacher, is a top student in our class.
A．the composition of hers
B．the composition of whom
C．her composition
D．whose composition
Student: I'm nervous.
Teacher:______. Betty, you'll finish it quickly.
A.What day is today
B.How are you today
C.What is the date today
D.What is today
Which of the following is TRUE of teacher’s correction of his student’s writing errors？ ()
A．It is good to correct all the errors
B．A teacher should write something on the papers to encourage his students
C．A teacher’s handwriting must be tidy and clear
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From the text we call infer that the writer is most likely to be a____
A．schoolboy
B．school teacher
C．schoolgirl
D．college student
