The Supply Pressure Gauge tells you:

How much pressure is in the air tanks.. Section 5.1: Supply pressure gauges tell you how much pressure is in the air tanks.

The Supply Pressure Gauge tells you:

ANSWER BREAKDOWN
  • A. Correct. Supply pressure gauges tell you how much pressure is in the air tanks.
  • B. Incorrect. "How much pressure you are applying." is not correct. Supply pressure gauges tell you how much pressure is in the air tanks.
  • C. Incorrect. "How hot the brakes are." is not correct. Supply pressure gauges tell you how much pressure is in the air tanks.
  • D. Incorrect. "The speed of the compressor." is not correct. Supply pressure gauges tell you how much pressure is in the air tanks.