I see you have already provided the correct answer. I will confirm it and add an explanation.
Answer:
. . . the product will be replaced immediately. (letter B)
Step-by-step explanation:
When filling in the blanks, we must pay attention to the context given by the passage or sentence that we are supposed to complete. In this case, our job is made easier by the fact that the options are words that have completely different meanings.
The passage is about a defective product, which means it is imperfect, that it is not functioning properly. When we buy something that does not work properly, the manufacturer of the product must give us another one, that is, they must replace it with one that does work. Therefore, the best option is letter B. replaced.