Why are plural nouns used in following situations?
1) Hat sections are popularly used energy absorption structures in automotives, ships, aircraft and aerospace vehicles.
2) …..black smoke that severely pollutes the air quality in cities .
3) With the development of industry, wear-resistant components gradually have gradually become the key parts of machines.
automotives, ships, aircraft and aerospace vehicles
Can I use them in singule form?
thank you very much