The answer is (b) and (c).

Now Sleepy is a class derived from the class Dwarf. So, it inherits all its
functions. For the class Sleepy to be instantiable, it should have NO pure
virtual function. Now, two of the functions that the class Sleepy inherits
from the class Dwarf are pure virtual. So, the class Sleepy has to provide
definitions for these two pure virtual functions, namely  whistle and work.