That- cannot modify people

[Neha.K]

Although some ornithologists contend that the precursors of birds are arboreal creatures that glide form tree to tree, other believe that they were runners whose front limbs evolved into wings

A. Although some ornithologists contend that the precursors of birds are arboreal creatures that glide form tree to tree

B. However it may be that some ornithologists contend that the precursors of birds were arboreal creatures that glide from tree to tree

C. Despite that the precursors of birds were, according to some ornithologists, arboreal creatures that glide from tree to tree.

D. Although some ornithologist content that the precursors of birds were arboreal creatures that glided from tree to tree.

E. According to some ornithologists gliding from tree to tree, the precursors of birds are arboreal creatures, that

In the above question, I can get the answer easily that it should be D among the choices given. However I was stuck on a point that "That can only modify things". Here "that" is modifying the creatures, which i do not consider as things. Is the usage of "that" correct in the question?

If there is a choice, where i am given a choice between usage of "that" or "who", as a word modifying creatures, should i choose "who"?

[tim]

what are creatures if not things? are they places? ideas?