Final answer:
Improvements to the canal zone that made it safe and attractive to workers were fumigation systems and mosquito nets, adequate housing and infrastructure, and sanitation measures.
Step-by-step explanation:
Three improvements to the canal zone that made it a safe environment to work in and attractive to workers were the introduction of fumigation systems and mosquito nets to reduce the spread of diseases like malaria and yellow fever, the construction of adequate housing and infrastructure such as cafeterias and warehouses, and the implementation of sanitation measures like fresh water pipes and sewer pipes.