GmatKiss wrote:Managing your irrigation system well and watering your grass wisely not only saves water, but helps to ensure the success of your lawn.

saves water, but helps to ensure the success of your lawn
saves water, but also help to ensure the success of your lawn
saves water, but the success of your lawn is more helpfully ensured
save water, but also help to ensure the success of your lawn
save water, but also the success of your lawn is more helpfully ensured

We need a VERB to connect with the subjects (COMPOUND SUBJECT - 'A and B')

Managing your irrigation system well and watering your grass wisely REQUIRE PLURAL VERB (SAVES - wrong); drop A/B/C

D vs E
NOT ONLY SAVE...BUT ALSO (require A VERB).. to make them parallel; Only D suits

E - save water, but also the success - IMPROPER PARALLELISM

IMO D

agreed (D) should be the answer.

confused betwn A and B..( i know not only but also is proper idiom but stilll smhw)
seems A.....

now i think D,,..

I believe that "D" is correct.

Verb Save and Help (plural for compound subject)
Parallel
Correct use if Idiom Not Only.......But Also

IMO D

Pay attention to where the underline begins and ends and start asking yourself: are there any patterns or clues here.
When an underline starts or ends on a verb, I immediately know I'm going to need to check subject-verb agreement or verb tense.

Compound Subject : Managing your irrigation system well and watering your grass wisely
Verb : "save" should be the verb

D vs E

Not only x but also y
x and y should be in same form.

not only save but also help

So ANS IMO D