Final answer:
Improvement generally refers to enhancements to real estate, such as streets, sewers, and building foundations; however, trade fixtures, which are equipment used in a business, do not fit this description as they are personal property.
Step-by-step explanation:
The word improvement is correctly applied to streets, a sanitary sewer system, and the foundation of a building as these elements can indeed be enhanced or upgraded to better serve the population. However, trade fixtures are not typically described by the word "improvement" in the same context. Trade fixtures refer to equipment or machinery used in a trade or business, which a tenant installs for their use in their leased premises. While they can be improved upon, they are personal property and not improvements to the real estate itself like the other options listed.