Final answer:
Young children and seniors are most likely to be killed in accidents while crossing the road. It is important for them to be accompanied by adults and follow proper road crossing protocols to minimize the risk of accidents.
Step-by-step explanation:
The question is asking about being careful while engaging in certain activities, as young children and seniors are at a higher risk of being killed in accidents related to these activities. Out of the given options, crossing the road is the most likely activity to be dangerous for young children and seniors. This is because they may not have the same level of awareness and caution as adults when it comes to traffic safety. It is important for them to be accompanied by adults and follow proper road crossing protocols to minimize the risk of accidents.