GMAT Sentence Correction (SC) | Re: Tilling means preparation of the soil to plant the seeds and keeping t

Another question on ||ism concept.

a)Tilling meanspreparation of the soil to plant the seeds andkeeping the soil in the best condition to help the crop grow until it is ready for harvesting -->||ism error.

b)Tilling means preparing the soil to plant the seeds and keeping the soil in the best condition to help the crop grow until it is ready to harvest

c)Tilling meanspreparation of the soil to plant the seeds andkeeping the soil in the best condition for helping the crop grow until