What is a threaded binary tree traversal?

(a) a binary tree traversal using stacks

(b) a binary tree traversal using queues

(c) a binary tree traversal using stacks and queues

(d) a binary tree traversal without using stacks and queues

Origin of the question is Threaded Binary Tree topic in chapter Binary Trees of Data Structures & Algorithms I

The question was posed to me during an interview.