Final answer:
The abstract noun in the sentence 'I have always admired your courage' is 'courage', which is an idea or quality, making it the correct answer.
Step-by-step explanation:
The abstract noun in the sentence "I have always admired your courage" is courage. An abstract noun refers to an idea, quality, or state rather than a concrete object. In this sentence, 'courage' represents the concept of bravery and is not something that can be touched or seen, which makes it an abstract noun. Therefore, the correct answer is b. Courage.