B is kind of a tricky answer choice to consider. The issue with it is that it isn't necessary that the number of fires detected by smoke alarms in homes has increased in order for the argument to be possible.
It tells us nothing about the likelihood of detecting a fire. It just gives us an absolute quantity.
Negating this doesn't weaken the argument either. If there are not more fires detected within homes by smoke detectors, this doesn't go against the idea that it no more likely to detect fires.
I hope this helps. Please let me know if you have any other questions.
