Read the passage from the Houston Chronicle about air quality in Houston in 2019.

“I’m surprised and disturbed that Houston’s air quality worsened in this year’s [American Lung Association ‘State of the Air’] report,” said Luke Metzger, director of Environment Texas. “The trend since 1999 had been one of steady progress and instead now it seems we are backtracking and that’s bad news particularly for the hundreds of thousands of people who have asthma or other vulnerable populations like senior citizens. . . .”

Current models estimate that more than 60 percent of ozone pollution is from cars, according to Raun, and to address that, the city is trying to encourage practices such as the use of mass transit and transitioning to fuel-efficient or low-emission vehicles.

Which statement best describes air quality in Houston since 1999?
A. Air pollution has been steadily increasing in Houston since 1999.
B. Air pollution has been steadily decreasing in Houston since 1999.
C. Air pollution has varied depending on climate conditions since 1999.
D. Air pollution has steadily decreased since 1999, before suddenly increasing.