Read the following technical passage describing a spacecraft maintenance protocol:
"Prior to servicing a spacecraft's hypergolic thruster manifold, technicians must execute a four-stage decontamination sequence. First, the isolation valves are closed and residual liquid is drawn down into the vacuum scavenger sump. Before introducing high-purity nitrogen for the intermediate purge, technicians must verify that line pressure drops below five millibars. Following the triple-cycle gaseous nitrogen flush, the moisture sensor port is uncapped to sample the residual vapor content. Only after the moisture baseline is confirmed acceptable do operators seal the vent manifold and apply a positive-pressure helium blanket to stabilize the system."
Based on the passage, match each procedural stage with its corresponding mandatory action.
- Initial fluid evacuationClose isolation valves and route residual propellant into the vacuum scavenger sump
- Pre-purge qualificationVerify line pressure drops below five millibars
- Post-flush evaluationUncap the sensor port to measure residual vapor content
- System stabilizationSeal the vent manifold and apply a positive-pressure helium blanket