Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. If pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species, then which of these terms are applicable?
1.    sympatric species
2.    prezygotic isolation
3.    postzygotic isolation
4.    allopatric species
5.    habitat isolation
6.    reduced hybrid fertility
A) 1 and 2
B) 2 and 4
C) 1, 3, and 6
D) 2, 4, and 5
E) 1, 2, 5, and 6

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