Which of the following consists of three words that refer exactly to the same thing in the passage

A．Carbon dioxide in the atmosphere carries heat into outer space so as to change the climate.
B．Carbon dioxide may escape into the greenhouse so that the Earth will be made warmer.
C．As carbon dioxide keeps heat from escaping into outer space, the Earth may become warmer.
D．Carbon dioxide may make the Earth warmer because it lets the heat escape into outer spac

A．as wage earners
B．both as manufacturers and consumers
C．both as workers and purchasers
D．as customers