SINGULAR and PLURAL - Be Careful

1.Some substantives use the verb always in the singular:
news
information
knowledge
progress
advice
measles
mumps
United States

2.For define quantity measures there is no plural, but for the indefinite ones there is plural.

a dozen -> eggs
hundred

BUT

dozens -> of eggs (indefinite)
hundreds

3.Look:

This jacket costs thirty dollars.It´s a thirty dollar jacket.
adjective


4.Invariable substantives:
deer
sheep
series
species
Portuguese
Japanese
Swiss