If the determination made driving the thirty days immediately proceeding any day have shown the percentage of inflammable gas to be below . . . . . . . . it shall be sufficient to make such determination, once in every . . . . . . . . days for so long as such does not exceed that percentage.

A. 0.8, 14

B. 0.6, 30

C. 0.8, 14

D. 0.7, 7

Answer: Option B