Methane (CH4, MW = 16 g/mole) produced during municipal wastewater treatment can be released from open-air tanks into the atmosphere. During a random sampling event, you determine that the air contains 0.05 ppm of methane. Which of the following could be a potential source of this methane?

A) Municipal wastewater treatment plants
B) Open-air tanks
C) Random sampling events
D) Atmosphere