Final answer:
High humidity can increase the risk of heat injuries. Option D. 90% is the correct choice. When humidity is high, sweat evaporation is impaired, which can lead to heat-related illnesses.
Step-by-step explanation:
High humidity can increase the risk of heat injuries. Among the answer options provided, the correct choice is option D. 90%. When the humidity is high, it becomes harder for sweat to evaporate, which impairs the body's ability to cool down. This can lead to heat-related illnesses, such as heat exhaustion or heat stroke.