Which of the following statements about air pollution is true?

a. rain water in the us is significantly more acidic today than it was in the 1970s.
b. air in the us is cleaner today than it was in the 1960s despite a larger population and more industry.
c. catalytic converters on cars convert carbon dioxide into ozone, vocs, and nox.

Afan that can provide air speeds up to 60 m/s is to be used in a low-speed wind tunnel with atmospheric air at 35 c. if one wishes to use the wind tunnel to study flat-plate boundary layer behavior up to reynolds numbes of re 10, what is the minimum plate length that should be used? at what distance from the leading edge would transition occur if the critical reynolds nurnber were rer,e = 5 × 105?