Question $6$

PM $2\mathrm{.}5$ refers to a $$ that can penetrate deep into the lungs.

A particle airborne for $2\mathrm{.}5$ hours

B particle that decreases net mortality by $2\mathrm{.}5\%$

C $2\mathrm{.}5$ micron $($um$)$ particle

D particle that increases net mortality by $2\mathrm{.}5\%$