OG161. A wildlife expert predicts that the reintroduction of the caribou into northern Minnesota would fail if the density of the timber wolf population in that region is more numerous than one wolf for every 39 square miles.
(A) would fail if the density of the timber wolf population in that region is more numerous than
(B) would fail provided the density of the timber wolf population in that region is more than
(C) should fail if the timber wolf density in that region was greater than
(D) will fail if the density of the timber wolf population in that region is greater than
(E) will fail if the timber wolf density in that region were more numerous than

在后面的解释中有“Density, an abstract "mass" noun, is logically construed with greater than”请问大家什么叫做"mass" noun？我的理解是，好像是不可数的用greater，可数名词则用more numerous than，大家是怎么理解的？多谢指教！