Fill in the blanks in each of the following statements:

a. In Java SE 8, an interface may declare                 —that is, public methods with con- crete implementations that specify how an operation should be performed.

b. As of Java SE 8, interfaces can include                 helper methods.

c. As of Java SE 8, any interface containing only one method is known as a(n)                 .

d. As of Java SE 9, any interface may contain                 instance and static methods.