Here are several function members of a class. Tell whether each may be used as an l-value, only, an r-value only or both. B is a class that has mutators.

a) ```
//declarations of these appear together in the //definition of class A
int& A::f( ){ /* */}
const int& A::f( )const{ /* */}
```

b) ```
const int& A::f( ){ /* */}
```

c) ```
const B A::f( ){ /* */}
```

d) ```
B A::f( ){ /* */}
```

In a) the first will be used if f() is used as an l-value, and the second implementation will be used if f() is used as an r-value.
In b) f() can be used as an r-value only.
In c) f() can be used as an r-value only and no mutators can be called on the return value.
In d) f() can be used as an r-value only, but mutators can be called on the return value