The test pressure for each pressure test conducted under 195.304 must be maintained throughout the part of the system being tested for ___ continuous hours at a pressure equal to ___ percent, of more, of the maximum operating pressure.

According to 49 CFR 195.304(a), the test pressure for each pressure test must be maintained for at least 4 continuous hours. The pressure must be equal to or greater than 1.25 times the maximum operating pressure, which translates to 125 percent.

Therefore, the blanks should be filled with 4 and 125.

The final answer is $\text{b. 4, 125}$