Part 77 Quiz - Part II Progress Indicator: Question 4 of 26 4.  The residual pressure warning consists of which of the following: Choices: First Alarm – approximately 75% O2, Second Alarm – approximately 25% O2 First Alarm – approximately 50% O2, Second Alarm – approximately 10% O2 First Alarm – approximately 75% O2, Second Alarm – approximately 5% O2 First Alarm – approximately 80% O2, Second Alarm – approximately 15% O2 None of the above