a) Example:

template <typename T1, typename T2>
T1& fun(T1& a, T2 b)
{
  return a += b;
}

b) The five special member functions are:

- default constructor
- copy constructor
- move constructor
- destructor
- copy assignment operator
- move assignment operator

c) Marking a constructor as explicit tells the compiler that it is not
   allowed to use this constructor for implicit type conversions.

d) The sizeof-operator returns the size in bytes of a type/object
while the sizeof...-operator returns the number of elements in a
variadic template/parameter pack.

e) When having constructed an object with the placement new-operator
or when destroying a non-trivial object that resides inside a union.