GMAT Sentence Correction (SC) | SC: To help preserve ancient Egyptian monuments threate

This question is testing us on Parallelism

To help preserve ancient Egyptian monuments threatened by high water tables, a Swedish engineering firm has proposedinstalling pumps ,perhaps solar powered, to lower the underground water level and digging trenches around the bases of the stone walls.

Here theBlue parts are the proposals of the Engineering firm (which are parallel)

1. Installing
2. Digging

installing pumpsperhaps solar powered ,to lower the underground water level

Here the
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