'Saves' coz it agrees with the singular subject 'One in five americans'
What about this :-
19. To help preserve ancient Egyptian monuments threatened
by high water tables, a Swedish engineering firm has
proposed installing pumps, perhaps solar powered, to
lower the underground water level and dig trenches around
the bases of the stone walls.(A) to lower the underground water level and dig trenches
(B) to lower the underground water level and to dig
trenches
© to lower the underground water level and digging trenches
(D) that lower the underground water level and that
trenches be dug
(E) that lower the underground water level and trench
digging
