Consequently, more than 100 cities in the United States still have levels of carbon monoxide, particulate matter, and ozone that（）legally established limits.

A.have been steadily increasing
B.has been steadily increased
C.has been steadily increasing
D.have been steadily increased

A.corporate
B.cooperating
C.operating
D.incorporating

A.used to go
B.were used to go
C.are used to go
D.ues to go