In California, a lack of genetic variation in the Argentine ant has allowed the species to spread widely; due to their being so genetically similar to one another, the ants consider all their fellows to be a close relative and thus do not engage in the kind of fierce intercolony struggles that limits the spread of this species in its native Argentina.
A.due to[W1] their being so genetically similar to one another, the ants consider all their fellows to be a close relative and thus do not engage in the kind of fierce intercolony struggles that limits
B.due to its being so genetically similar the ant considers all its fellows to be a close relative and thus does not engage in the kind of fierce intercolony struggles that limit
C.because it is so genetically similar, the ant considers all its fellows to be close relatives and thus does not engage in the kind of fierce intercolony struggles that limits
D.because they are so genetically similar to one another, the ants consider all their fellows to be close relatives and thus do not engage in the kind of fierce intercolony struggles that limit
E.because of [W2]being so genetically similar to one another, the ants consider all their fellows to be a close relative and thus do not engage in the kind of fierce intercolony struggles that limits
为什么C正确呢？Ｃ项最后那个limites是修饰struggles的吗？如果是，那struggles是复数，limit该用复数吧？？百思不解。 | 
