The argument says that Southern Airways has a far worse safety record that Air Dacentaria
Therefore, although Air Dacentaria is slightly more expensive, I will choose it over Southern Airways for my flight from Pederton to Dacenta.

Since the overall safety is worse for the SA => also on a specific flight the safety is worse.This is the argument of the text.

The correct answer will destroy this connection somehow: will show that the data is not reliable or that there are distortions, and so on...

B and E...

B. Most Southern Airways flights, ut not its flight from Pederton to Dacenta, use Sarmouth airport, which because of its mountainous location is one of the world's most dangerous.
B says that the overall rate of accidents is overestimated because SA uses a particular airport that is dangerous. So we can infer that, if SA stops using that airport, its safety level would be higher than that of the other company; and because the person will not flight in that airport, the argument is weakened.(This answer shows that the overall data is not a reliable indicator because suffers from the low safety of a single airport).

E. Although the frequency of accidents is greater on Southern Airways, on both airlines the proportion of flights that have accidents is very small.
E does not affect the conclusion. "on both airlines the proportion of flights that have accidents is very small" => when comparing different companies the most important stats are the percentages (not the overall number), and E says that under this point of view there is no difference between the two companies.