C++ template class and inheritance

Possible Duplicates:
[FAQ] Why doesn't a derived template class have access to a base template class' identifiers? Problem with protected fields in base class in c++
cannot access data member in a class template

Following code gives me compilation error. What is wrong?

struct Base {
   int amount;
};

template<class T> struct D1 : public Base {
};

template<class T>
struct D2 : D1<T> {
  void foo() { amount=amount*2; /* I am trying to access base class data member */ };
};

int main() {
  D2<int> data;
};


test.cpp: In member function 'void D2<T>::foo()':
test.cpp:11: error: 'amount' was not declared in this scope

How to fix this?

thanks