In an effort to reduce the number of fires started by cigarettes, a major tobacco company is test-marketing a cigarette in which thin layers of extra paper are used to decrease the amount of oxygen entering the cigarette, thereby slowing the rate at which it burns and lowering the heat it generates.

a. in which thin layers of extra paper are used to decrease the amount of oxygen entering the cigarette, thereby slowing

b. in which they use thin layers of extra paper in decreasing the amount of oxygen entering the cigarette, which slows

c. that uses thin layers of extra paper to decrease the amount of oxygen when it enters the cigarette, thereby slowing

d. for which thin layers of extra paper are used to decrease the amount of oxygen that enters the cigarette, and thereby slowing

e. using thin layers of extra paper in decreasing the amount of oxygen entering the cigarette, which slows