Maneuverable strollers are disclosed herein. transistors connected to a first current source and a second differential pair of NMOS transistors connected to a second current source are mutually connected at the differential output terminals, and a capacitor is connected between the connection nodes of the respective differential pairs and current sources. Each contactor includes a mass transfer vessel having a mixing section. If this is the case, the measured quantity is the drawn-in air mass, and the signal-range check is performed, provided that the engine operating state and thus the drawn-in air satisfies specifiable conditions. A suction source is positioned within the suction source housing to define an annular exhaust flow passageway surrounding the suction source from the housing closed end to the housing open end.