(C)

@Samir, Let's look at the argument. State researchers have found that since the oil price increases, there has been a decline in home energy consumption. They concluded that almost all of the decline has been achieved through reduced standards of living and changes in the way spend their time. (A) says "sales of portable heaters rose as families concentrated their winter activities in certain rooms." This fact clearly supports the fact that one's standard of living has gone down if they cannot afford to heat their whole house and instead, use a portable heater to heat only a limited space. Since energy consumption by a portable heater is less than a center heater, and the use of portable heaters is associated with a reduced standard of living, this fact supports the conclusion. Does this make sense? Let me know if you have any further questions.

@Julie, My apologies for accidentally posting a response from a different thread. The support for option (C) is found on lines 36-37 "both interpreted what they had heard and determined matters of fact." (C) paraphrases this line. Let me know if you have any further questions.