637 Several studies have found that the coronary patients who exercise most actively have half or less than half the chance of dying of a heart attack as those who are sedentary.

(A) have half or less than half the chance of dying of a heart attack as those who are sedentary

(B) have half the chance, or less, of dying of a heart attack than those who are sedentary do

(C) have half the chance that they will die of a heart attack, or less, than those who are sedentary do

(D) are at least fifty percent less likely to die of a heart attack as those who are sedentary（E）

(E) are at least fifty percent less likely than those who are sedentary to die of a heart attack

看过前人的讨论了，但是还是有一点不明白，请大家指教：B和C中的or less 是不是插入语呢？大全简注上解释是“，or less”是个插入语，因此than没有比较的对象了；而另一种说法是B、C错在表达不够简洁上，即at least less than优于as...as, or less的表达（本题虽然不是这种标准形式，但类同）

请NN们确认一下