单项选择题
A. The elements in the collection are ordered.
B. The collection is guaranteed to be immutable.
C. The elements in the collection are guaranteed to be unique.
D. The elements in the collection are accessed using a unique key.
E. The elements in the collections are guaranteed to be synchronized.
单项选择题 Youneedtostoreelementsinacollectionthatguaranteesthatnoduplicatesarestoredandallelementscanbeaccessedinnaturalorder.Whichinterfaceprovidesthatcapability？（）
填空题 3. string foo = “ABCDE”； 4. foo.substring（3）； 5. foo.concat（“XYZ”）； 6. Type the value of foo at line 6.（）
单项选择题 1. public class X （ 2. public object m （） { 3. object o = new float （3.14F）； 4. object [] oa = new object [1]； 5. oa[0]= o； 6. o = null； 7. return oa[0]； 8. } 9. } When is the float object created in line 3， eligible for garbage collection？（）