单选题Given： Which code， inserted at line 16， will cause a java.lang.ClassCastException？（）A Alpha a = x；B Foo f = （Delta）x；C Foo f = （Alpha）x；D Beta b = （Beta）（Alpha）x；

A.Foo.beta（）isavalidinvocationofbeta（）.

B.Foo.alpha（）isavalidinvocationofalpha（）.

C.Methodbeta（）candirectlycallmethodalpha（）.

D.Methodalpha（）candirectlycallmethodbeta（）.

A.int foo() { /* more code here */ }

B.void foo() { /* more code here */ }

C.public void foo() { /* more code here */ }

D.private void foo() { /* more code here */ }

E.protected void foo() { /* more code here */ }

14 Alpha buys goods from Beta. At 30 June 2005 Beta’s account in Alpha’s records showed $5,700 owing to Beta.

Beta submitted a statement to Alpha as at the same date showing a balance due of $5,200.

Which of the following could account fully for the difference?

A Alpha has sent a cheque to Beta for $500 which has not yet been received by Beta.

B The credit side of Beta’s account in Alpha’s records has been undercast by $500.

C An invoice for $250 from Beta has been treated in Alpha’s records as if it had been a credit note.

D Beta has issued a credit note for $500 to Alpha which Alpha has not yet received.

如果类Alpha继承了类Beta，则类Alpha称为派生类，类Beta称为【 】类。

10.interfaceFoo{}11.classAlphaimplementsFoo{}12.classBetaextendsAlpha{}13.classDeltaextendsBeta{14.publicstaticvoidmain（String[]args）{15.Betax=newBeta（）；16.//insertcodehere17.}18.}Whichcode，insertedatline16，willcauseajava.lang.ClassCastException？（）

A.Alphaa=x；

B.Foof=（Delta）x；

C.Foof=（Alpha）x；

D.Betab=（Beta）（Alpha）x；

A.Alpha a = x;

B.Foo f = (Delta)x;

C.Foo f = (Alpha)x;

D.Beta b = (Beta)(Alpha)x;

A.packagecom.；

B.importcom.x；

C.packagecom.x；

D.importcom.x.Alpha；