Final answer:
The correct word to fill in the blank is 'inaudible.'
Explanation:
Audible means capable of being heard, while inaudible means not capable of being heard. In the context provided, the sentence 'my grandfather spoke so quietly that his words were almost _____' indicates a situation where his words were hard to hear, making the correct choice inaudible.
Learn more about Vocabulary here:
https://brainly.com/question/28932775
