25. Explain in some detail two preventive maintenance measures that are used to keep constructed structures in good working order.

The goal of maintenance is to keep products in good condition and good working order. For example, clothing and dishes are washed to maintain their usefulness and extend their life. Also, filters in furnaces and air conditioning units are changed so the units function properly. The oil in automobile engines is changed to maintain the oil’s ability to lubricate moving parts. Furthermore, locomotives and buses are serviced to maintain their performance. Most maintenance is done on a schedule which is designed to keep the product working properly. Therefore, it is sometimes called preventive maintenance, and is designed to prevent breakdowns.

I wasn't sure exactly how to answer this question. This is what I found in my book.

It sounds great, but frankly, I don't know what is meant by constucted structures. What would be a not-constructed structure?