Based on the provided information from the article, the most accurate inference a reader can make about thermometer pills is:
A The effectiveness of one thermometer pill is temporary.
The article discusses that thermometer pills are used to monitor body temperature during high heat events to prevent heatstroke, suggesting their use is specific to the time they are ingested and monitored. Once the monitoring is completed, the effectiveness pertains only to that specific usage scenario, making it temporary. The other options (B, C, and D) regarding pricing trends and permanent effectiveness do not have clear support from the text provided.