The relevant information is: Flash-gas may be detected in the system by the observation of bubbles or gas presence in the liquid line, or the foamy aspect of the fluid.
This justifies what answer for what question? Q & A: 
Passage: Flash-gas may be detected in the system by the observation of bubbles or gas presence in the liquid line, or the foamy aspect of the fluid. Depending on the location of the glass: this may also indicate an overwhelmed condenser, and the nonobservance of these at the glass is n't definite of the nonoccurrence of flash-gas in the liquid line.

Question: Based on this passage, how can flash gas in the liquid line be identified?
by the observation of bubbles or gas presence in the liquid line , or the foamy aspect of the fluid