What does the diaphragm of the Airspeed Indicator contain?

The diaphragm of the Airspeed Indicator contains ram pressure, which is the dynamic pressure created as air flows into the pitot tube during flight. This ram pressure is crucial because it is compared against the static pressure that comes from the static port to determine the aircraft's airspeed. As the ram pressure increases with the aircraft's speed, the diaphragm expands or contracts accordingly. This movement then drives the needle on the airspeed indicator to display the current airspeed.

The other options do not accurately describe the function of the diaphragm within the Airspeed Indicator; static pressure does not provide the dynamic measure needed for the display, aneroid wafers are components found in altimeters, and a magnetometer is associated with navigation and direction sensing, not airspeed measurement.