One question of sentence completion

xxxiiiaaattt
Sat, 09 Apr 2011 05:09:08 +0000

Because insect communities serve as a sort of barometer, (. )conditions in their (. ),an entomologist’s analysis of the insect species in a handful of soil can reveal much about the ecosystem.
A: preserving. habitat
E: registering. environment
(I have already eliminated the other choices, the answer is E, but registering doesn’t make sense to me.)