The second method does not require pressurization of the pneumatic crossover manifold, but utilizes an external air source connected to the air charging valve manifold to pressurize the reservoirs for ground maintenance.
A Pressurization of the pneumatic crossover manifold and use of an external air source connected to the air charging valve manifold to pressurize the reservoirs for ground maintenance is the second method.
B You can use the second method to pressurize crossover manifold and use an external air source connected to the air charging valve" manifold to pressurize the reservoirs for ground maintenance.
C The second method is that it is not necessary to pressurize the pneumatic crossover manifold but to use an external air source connected to the air charging valve manifold to pressurize the reservoirs for ground maintenance.