<e1>Diatoms</e1> have an external <e2>skeleton</e2> of silica and silicon may therefore be a limiting element to diatom population growth.
Diatoms have an external
Diatoms have an external skeleton of silica and silicon may therefore be a limiting element to diatom population growth.
<triplet> Diatoms <subject> skeleton <object> Component-Whole(e2,e1)