When to use verb+ing or to+verb

[MBA]

Hi,

Please suggest me when to select answer choices with verb+ing format and when to select the Verb format.For example

if the sentence is ---In a plan to stop the erosion of east coast beaches,the army corps of engineers proposed building parallel to shore a breakwater of rocks that would rise six feet abve the waterline and act as a buffer,so that it absorbes the energy of crashing waves and protecting the beaches.

why the option--act as a buffer,absorbing---is correct ?

why not---acting as a buffer,absorbing--is wrong?

Thanks for your help

[pharmxanthan]

Parallelism.

to shore......to act

NOT to shore....to acting

[susantaiitk]

In a plan to stop the erosion of east coast beaches,the army corps of engineers proposed building parallel to shore a breakwater of rocks that would rise six feet abve the waterline and act as a buffer,absorbing the energy of crashing waves and protecting the beaches

I think would rise is in parallel with act ..... i guess would act is not required as it would make it wordy.

"absorbing the energy of crashing waves and protecting the beaches" is a clause describing how the breakwater rocks act as a buffer .. I think we use verb+ing usually in clauses like this.

[MBA]

Thanks.....for pointing out that the correct answer is due to parallelism.Then why below given example has different answer

Scientists have recently discovered what could be the largest and oldest living oraganism on earth,a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single ferlilized spore some 10,000 years ago and extending for more than 30 acres in the soil of Michigan forest.

Why the correct answer is extending

and not the parallel ......spawned.........and extended

or ......that is an interwoven......and extends....

[atsu4320]

I think "tentacles" are "spawned" and "extending." It is sort of the former is passive (by a single ferlilize ---) and later is active (tentacles extend itself). This is more like a mixed modifier problem combined with parallelism rather than just a simple parallelism problem.

I guess someone else should be able to explain with a better way.

Thanks.....for pointing out that the correct answer is due to parallelism.Then why below given example has different answer

Scientists have recently discovered what could be the largest and oldest living oraganism on earth,a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single ferlilized spore some 10,000 years ago and extending for more than 30 acres in the soil of Michigan forest.

Why the correct answer is extending

and not the parallel ......spawned.........and extended

or ......that is an interwoven......and extends....