Select the best version of the underlined part of the sentence. The first choice is the same as the original sentence. If you think the original sentence is best, choose the first answer.
Many gardeners are now making their own backyard compost, (which is not only cheap, but also helps to cut down on landfill waste.)
a. which is, not only cheap, but also, helps to cut down on landfill waste
b. which is not only cheap, but also helps to cut down on landfill waste
c. which is not only cheaper, but also cuts down on landfill's waste
d. which is not only done cheaply, but is also cutting down on landfills wastes