问个prep里的句子的理解

Traveler: 
Southern Airways has a far worse safety record than Air Dacentaria over
the past few years, in terms of both the frequency of accidents and the
severity of accidents.  Therefore,
although Air Dacentaria is slightly more expensive, I will choose it over
Southern Airways for my flight from Pederton to Dacenta, since it is worth
paying extra to have a safer flight.

Which of the following, if true, casts the
most serious doubt on the traveler's argument?

(A) Air Dacentaria's flight from Pederton
to Dacenta is nonstop, whereas Southern Airways' flight touches down in Gorinda
on the way.

(B) Most Southern Airways flights, but not
its flight from Pederton to Dacenta, use Sarmouth airport, which because of its
mountainous location is one of the world's most dangerous.

(C) For its flights from Pederton to
Dacenta, Southern Airways uses a different model of airplane, with a smaller
capacity, than the model Air Dacentaria uses for its flights on the same route.

(D) Only in the last few years has the cost
of flying from Pederton to Dacenta been more expensive on Air Dacentaria than
on Southern Airways.

(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 选项应该怎么翻译, "on both airlines the proportion of flights that
have accidents is very small." both不是只能用来表示两个吗? airlines显然不止两条吧, 那或是指两个公司? 怎么理解这个意思呢?