For a group experiment, your science class measured the fine-particulate concentrations in the air at random places around campus, and estimated a sample average of 22 μg/m3 (micrograms per cubic meter). If 144 readings were taken, and the standard deviation of the sample measurements was 4 μg/m3, you are 99.7% confident that actual concentration of fine particulates at the school is __________ .

A.
21.3 μg/m3 – 22.7 μg/m3

B.
18 μg/m3 – 26 μg/m3

C.
21.7 μg/m3 – 22.3 μg/m3

D.
21 μg/m3 – 23 μg/m3