A typical gasoline–powered lawn mower emits about as much air–polluting material per hour of use as does an automobil...

Irina on September 25 at 10:12PM

@elsaleh,

(D) is incorrect because it weakens the argument. The argument concludes that people can help reduce air pollution by switching to electric mowers, whereas (D) suggests that people could instead buy a redesigned gasoline mower to reduce pollution.

Let me know if you have any further questions.